Installation and Maintenance Manual
SuperMod Forced Draft Gas Fired Furnace
on McQuay Applied Rooftop Systems
IM 685-2
Group: Applied Systems
TM
Part Number: IM685
Date: February 2007
HT***A* with RM7897A Flame Safeguard
© 2007 McQuay International
IM 685-2
1
When writing to McQuay for service or replacement parts, refer to the model number of the unit as stamped on the serial plate,
attached to the unit. If there is an in-warranty failure, state the date of installation of the unit and the date of failure along with an
explanation of the malfunctions and the description of the replacement parts required. Parts are warranted for ninety (90) days
unless covered by original unit warranty.
Table of Contents
General
Warranty Exclusion .......................................................... 3
Ventilation and Flue Pipe Requirements .......................... 3
Factory Mounting ............................................................. 3
Factory Checkout ............................................................. 3
Flame Safeguard
Keyboard Display Module ..............................................12
Operation.........................................................................12
Normal Start-Up..............................................................12
Service
General ............................................................................13
Gun Assembly.................................................................13
Gun Assembly Removal and Installation .......................13
Flame Rod Adjustment ...................................................13
Flame Rod Installation ....................................................13
Ignition Electrode Adjustment ........................................13
Air & Gas Adjustments...................................................14
Gas Supply Pressure .......................................................14
High Pressure Regulator .................................................14
Gas Adjustment...............................................................14
Air Adjustments ..............................................................14
Air and Gas Control Linkage ..........................................14
Actuator Crankarm..........................................................15
Switch Adjustments ........................................................15
Altitude Considerations ..................................................15
Gas Valve Pressure Regulator Adjustment .....................16
Adjustment Procedure for Parallel Valves ......................16
Check Manifold Pressure at Minimum Rate...................16
Combustion Testing ........................................................17
Verify Input Rate.............................................................17
Check CO2, CO and Stack Temperature .........................17
Cleaning Heat Exchanger (Models 032-200) .................17
Cleaning Heat Exchanger (Models 020-025) .................18
Leakage Symptoms .........................................................18
Checking for Leaks .........................................................18
Causes of Failures ...........................................................18
Replacing Heat Exchanger..............................................19
Furnace Condensation ....................................................19
Rear Inspection Cover.....................................................19
Combination Fan and Limit Control...............................20
Installation
General ............................................................................. 3
Flue Box ........................................................................... 3
Wind Deflector ................................................................. 4
Electrical........................................................................... 4
Gas Pressure Requirements.............................................. 4
Gas Piping ........................................................................ 4
Valve and Regulator Venting............................................ 5
Normally Open Vent Valve .............................................. 5
Gas Piping Routing into Unit ........................................... 6
On-the-Roof Piping (Models 020-140) ........................ 6
Through-the-Curb Piping (Models 020-140)................ 6
Typical Piping Connections .......................................... 6
Gas Piping (Models 150-200)....................................... 7
Gas Piping Within the Vestibule................................... 7
Field Gas Piping Required............................................ 7
Condensate Drain.......................................................... 7
Vestibule (Models 150-200) ......................................... 7
Start-Up & Operating Procedures
Start-Up Responsibility .................................................... 8
Start-Up Procedure ........................................................... 8
Before Start-Up ................................................................ 8
About This Burner............................................................ 8
Prepurge is Low-High-Low .......................................... 8
Low Fire Start ............................................................... 8
“Pilot” is Main Flame Modulated Down
to Pilot Rate ................................................................ 8
Set Control System to Enable Heating ......................... 8
Start-Up Preliminary ........................................................ 8
Preliminary “Dry” Run..................................................... 9
Flame Start-Up ................................................................. 9
Modulate Firing Rate ....................................................... 9
Combustion Tests ........................................................... 10
Cycle the Unit................................................................. 10
Record Data.................................................................... 10
Maintenance
Monthly, Twice Yearly, Yearly........................................20
Flame Safeguard
Characteristic and Operation...........................................20
Troubleshooting Chart .................................................22
References
Typical Sequence of Operation .......................................11
Typical Parts List - 60 Hz..............................................27
Capacities & Adjustments Table ................................ 28
Performance & Service History.................................. 29
McQuay Model Designation
Furnace
Model
Output
Capacity
(MBh)
20
25
32
40
50
64
65
79
80
100
110
140
150
200
200
250
320
400
500
640
650
790
800
1000
1100
1400
1500
2000
SERVICED BY:
TELEPHONE NO:
INSTALLATION DATE:
Installer: Leave this manual with owner. It is to be posted and maintained in legible condition.
2
IM 685-2
General
This forced draft gas burner is specifically designed for use
with the furnace on McQuay applied rooftop heating and air
conditioning units which are for outdoor installation only.
Each model size has unique burner head components to tailor the shape of the flame to each particular stainless steel
combustion chamber, to match the capacity requirement, and
to offer a desirable turndown potential when arranged for
modulation. This is a forced draft burner with a high pressure combustion air fan and will operate against pressure.
This eliminates the need for draft inducers, chimneys, draft
hoods, barometric dampers, and Breidert caps.
Warranty Exclusion
Warranty is void if the furnace is operated in the presence of
chlorinated vapors, if the airflow through the furnace is not
in accordance with rating plate, or if the wiring or controls
have been modified or tampered with.
WARNING
Units equipped with gas heating must not be operated
in an atmosphere contaminated with chemicals which
will corrode the unit such as halogenated hydrocarbons, chlorine, cleaning solvents, refrigerants, swimming pool exhaust, etc. Exposure to these compounds
may cause severe damage to the gas furnace and result
in improper or dangerous operation. Operation of the
gas furnace in such a contaminated atmosphere constitutes product abuse and will void all warranty coverage
by the manufacturer. Questions regarding specific contaminants should be referred to your local gas utility.
Ventilation & Flue Pipe Requirements
The McQuay applied rooftop unit is equipped with an outdoor air louver to supply adequate combustion air. The unit
also has a flue outlet assembly and requires no additional
chimney, flue pipe, Breidert cap, draft inducer, etc.
Factory Mounting
This burner and gas train have been installed and wired at
the factory. See “Gas Piping” on page 4. Also note that models 150 through 200 have the burner removed for shipment.
See “Vestibule (Models 150 thru 200)” on page 7.
Factory Checkout
This complete heating plant was fired and tested at the factory. It was adjusted to the required capacity and efficiency.
Modulating air and gas linkages, pressure regulators, and
stops were adjusted for proper operation at all firing levels.
The unit was fired through several complete start-up through
shutoff sequences to check operation. A check was made of
the air switch, gas pressure switch, high limit operation, and
combustion characteristics including CO2 and CO (at several
firing rates on modulating burners).
IM 685-2
If the burner was specified for operation at higher altitudes,
combustion air adjustments were compensated to result in
proper settings at the higher altitude. This checkout normally eliminates on-the-job start-up problems; however, the
equipment is subject to variable job conditions and shipping
shocks can change adjustments, cause damage, and loosen
connections and fasteners. Therefore, it is necessary to go
through the complete start-up procedure even though the
unit may appear to be operating properly.
Installation
General
The installation of this equipment shall be in accordance
with the regulations of authorities having jurisdiction and all
applicable codes. It is the responsibility of the installer to
determine and follow the applicable codes. Sheet metal
parts, self-tapping screws, clips, and such items inherently
have sharp edges, and it is necessary that the installer exercise caution. This equipment is to be installed by an experienced professional installation company that employs fully
trained and experienced technicians.
Flue Box (see Figure 1)
The flue box is not installed at the factory because it would
increase the width of the unit beyond the allowable shipping
width. All holes are prepunched, the fasteners are furnished
and everything is shipped in a box in the burner section. On
Models 150 through 200 it is shipped in the same crate as
the vestibule. Remove and discard the shipping cover
installed over the furnace tube outlets before installing the
flue box.
1. Remove the screws (2) in the casing of the unit that line
up with the bottom lip holes of the flue box tube sheet
(3). These screws will later be replaced, at which time
they will also attach the bottom of the flue box to the
unit.
2. Install the flue box tube sheet (3), attaching top to roof
dam strip with screws (1). Do not attach bottom at this
time.
3. Apply a 1/8 to 3/16 inch bead of high temperature silicone around each tube to seal it to the flue box tube sheet
(3) and prevent condensate from running back toward the
unit along the outside of the tube. Also apply a bead of
high temperature silicone to seal both sides to the bottom
of the flue box wrapper (4), being careful not to obstruct
the square drain holes in each front corner.
4. Install flue box wrapper sheet (4) by sliding it up from
below so as not to disturb the silicone seal described in 3
above. Attach with side screws (5). At this time reinstall
bottom screws (2).
3
Figure 1. Flue Box
1
Electrical
The McQuay burner receives its electrical power from the
main unit control panel. No additional power wiring must be
routed to the burner. The sequencing of the burner is also
controlled through this panel and therefore is factory wired.
No additional wiring will be required. Note that models 150
through 200 furnaces require reassembly of some electrical
connections as the burner is removed for shipment.
WARNING
Improper installation, adjustment, alteration, service or
maintenance can cause property damage, severe personal injury or death. Read the installation, operating
and maintenance instructions thoroughly before installing or servicing this equipment.
If you smell gas:
1. Open windows and ventilate area thoroughly.
2. Don’t touch electrical switches.
3. Eliminate open flames, pilot lights, arcing or sparking
equipment, or other sources of ignition.
4. Evacuate the area.
5. Immediately call your gas supplier from a different
area.
Wind Deflector (see Figure 2)
The wind deflector is not installed at the factory because it
would increase the width of the unit beyond the allowable
shipping width. The deflector is shipped in a box in the
burner section. Install the wind deflector over the combustion
air intake opening of the burner compartment before operating the burner. Use inner hinge screws on top hinged door.
Side hinged doors have holes for mounting (see Figure 5).
Models 020 and 025 have a different style wind deflector. It
mounts on the door and has a top opening flush with the roof
of the unit (see Figure 14).
Figure 2. Wind Deflector (Models 032 thru 140)
Tube Ends
3
Flue Box
Tube Sheet
4
Flue Box
Wrap
Gas Pressure Requirements
The pressure furnished to the combination gas control(s)
must not exceed 13.9 in. W.C. When the supply pressure is
above 13.9 in. W.C., a high pressure regulator must precede
the combination gas control(s). The inlet gas pressure cannot
exceed the maximum pressure rating of the high pressure
regulator and the outlet pressure must be such that it will
furnish gas to the appliance pressure regulator within the
pressure range mentioned above, preferably at 7.0 in. W.C.
when firing at maximum rate.
Gas Piping
The connection size at the burner is shown in Table 7 under
Column 13 thru 15. Gas piping must be sized to provide the
minimum required pressure at the burner when the burner is
operating at maximum input. Consult the appropriate local
utility on any questions on gas pressure available, allowable
piping pressure drops, and local piping requirements.
Install all piping in accordance with the National Fuel Gas
Code (ANSI Z223.1), (NFPA 54-1999) and any applicable
local codes.
Wind Deflector
Hinge Inner
Screw
Burner
Access
Door
4
Do not use and store gasoline or other flammable
vapors or liquids in open containers near this appliance
or in areas sharing ventilation with it.
It is very important that the proper size piping be run from
the meter to the gas burner without reductions. Undersized
piping will result in inadequate pressure at the burner. The
pressure will be at its lowest when it is needed the most, at
times of maximum demand. Therefore, it can cause intermittent hard-to-find problems because the problem may have
left before the service technician has arrived. Avoid the use
of bushings wherever possible.
IM 685-2
Remove all burrs and obstructions from pipe. Do not bend
pipe; use elbows or other pipe fittings to properly locate
pipe. A drip leg must be installed in the vertical line before
each burner such that it will not freeze. Install unions so gas
train components can be removed for service. All pipe
threads must have a pipe dope which is resistant to the
action of LP gas. After installation, pressurize the piping as
required and test all joints for tightness with a rich soap
solution. Any bubbling is considered a leak and must be
eliminated. Do not use a match or flame to locate leaks.
Valve & Regulator Venting
Valve diaphragm vents, pressure regulator vents, and pressure switch vents are located in the outdoor burner vestibule
and therefore vent tubing is not run to the outside of this vestibule. If local regulations require that this be done, it is a
part of the field gas piping hookup. Remove any plastic protector plugs from regulator and valve vents.
Normally Open Vent Valve
Vent valves such as required by IRI for over 1000 MBH
input units must always be routed to the outdoors. This is
field piping.
Table 1. Capacity of pipe natural gas (CFH)
PIPE
LENGTH (FT.)
10
20
30
40
50
60
70
80
90
100
125
150
175
200
WITH PRESSURE DROP OF .3" W.C. & SPECIFIC GRAVITY OF 0.60
PIPE SIZE-INCHES (IPS)
½
¾
1
1¼
1½
2
2½
132
278
520
1050
1600
2050
4800
92
190
350
730
1100
2100
3300
73
152
285
590
890
1650
2700
63
130
245
500
760
1450
2300
56
115
215
440
670
1270
2000
50
105
195
400
610
1150
1850
46
96
180
370
560
1050
1700
53
90
170
350
530
990
1600
40
84
160
320
490
930
1500
38
79
150
305
460
870
1400
34
72
130
275
410
780
1250
31
64
120
250
380
710
1130
28
59
110
225
350
650
1050
26
55
100
210
320
610
980
3
8500
5900
4700
4100
3600
3250
3000
2800
2600
2500
2200
2000
1850
1700
4
17500
12000
9700
8300
7400
6800
6200
5800
5400
5100
4500
4100
3800
3500
Note: Use multiplier below for other gravities and pressure drops.
Table 2. Specific gravity other than 0.60
SPECIFIC GRAVITY
0.50
0.60
0.70
0.80
0.90
1.00
IM 685-2
MULTIPLIER
1.100
1.000
0.936
0.867
0.816
0.775
Table 3. Pressure drop other than 0.3"
PRESSURE
DROP
0.1
0.2
0.3
0.4
0.6
0.8
MULTIPLIER
PRESSURE
MULTIPLIER
0.577
0.815
1.000
1.16
1.42
1.64
1.0
2.0
3.0
4.0
6.0
8.0
1.83
2.58
3.16
3.65
4.47
5.15
5
Gas Piping Routing Into Unit
On-The-Roof Piping (Models 020-140)
1. Remove knockout (1) at corner of burner vestibule door
and saw out corner of door. See Figure 3b. Make saw cuts
(2) tangent to round hole and square with door edges.
2. Install pipe corner plate (3) on vestibule, locating on prepunched holes. See Figure 3c. This part is shipped inside
the vestibule.
3. Route gas supply pipe through hole. Carefully plan pipe
route and fitting locations to avoid interference with
swinging of doors, etc.
Through-The-Curb Piping (Models 020-140)
1. Remove bottom access panel (5). See Figure 3c.
2. Remove knockout (4) and make an opening (6) through
bottom deck directly below knockout hole.
3. Route gas pipeline through these openings and seal them
off with suitable grommets (7).
See Figure 3a Section A-A.
4. Replace bottom access panel (5).
Figure 3c.Pipe Corner Plate
Figure 3a. Pipe Routing
4
7
A
5
3
4
6
7
A
2
1
Gas Supply
See Figure 3c
2
Section A-A
Figure 3b. Knockout
Typical Piping Connections
Figure 4. Connections
FSG
A
C
C
D
D
With Shutoff Cock
Folded Back
Figure 4b.
With Shutoff Cock
In Front
A
B
E
Figure 4a.
A = Shutoff Cock (ball valve)
B = Union - Furnished.
C = Gas Pipe - Routed in through front
D = Gas Pipe - Routed in through curb
E = Factory Piped Gas Trains
6
IM 685-2
Gas Piping (Models 150 thru 200)
The gas piping cannot be routed up to the burner from
within the curb on Models 150 through 200. Gas piping
must be routed across the roof to under the burner vestibule, or a pitch pocket can be provided there. The installer
must cut a hole in the bottom panel of the overhanging
burner vestibule through which to route the gas line up to
the burner gas train. The bottom panel of the vestibule is
at approximately the same elevation as the top of the curb.
accessible from outside the unit, that valve must be relocated
or an additional valve added. In locating such a valve, it is to
be readily accessible and located such that no obstructions
interfere with operation of the handle.
Condensate Drain
All units are equipped with a 3/4" I.P. condensate drain pipe
projecting from the back side of the furnace section (see Figure
13 and Figure 14) and the flue box corners (see Figure 1). If
applicable codes or regulations require, this can be routed to a
drain. A trap is not recommended and heat tape or some other
method of freeze protection is required.
Gas Piping within the Vestibule
The gas piping layout within the vestibule will vary
according to the complexity and size of the gas train relative to the available room within the vestibule. As an
example, a gas train with a high pressure regulator and an
extra safety shutoff valve (when required for IRI, etc.) will
require careful use of the available space. The examples
shown in Figure 4 indicate typical piping layouts.
Vestibule (Models 150 thru 200)
These two furnace sizes exceed the allowable shipping width
and for this reason the burner is disconnected and removed for
shipment. A sheet metal vestibule weather enclosure is also
disassembled for shipment. At installation the burner must be
re-mounted, the tagged electrical connections re-attached, and
the vestibule re-assembled and mounted as shown in Figure 5.
These items are packed in a crate and shipped as a separate
item.
Field Gas Piping Required
The gas train components have all been factory installed
and require only a connection to the supply gas line. The
manual shutoff valve is located within the burner vestibule. If local codes require a manual shutoff valve that is
Figure 5. Vestibule
Door
Side Panel
Top Panel
Hinge
#10 Screw
Cut Gas Line Opening
Fasten Wind Deflector
To Door With #10 Screws,
(Door & Wind Defletor
Part of Vestibule Kit)
Side Panel,
With Latch
Door
Bottom Panel
IM 685-2
7
Start-Up & Operating Procedures
Start-Up Responsibility
The start-up organization is responsible for determining that
the furnace, as installed and as applied, will operate within
the limits specified on the furnace rating plate.
1. The furnace must not exceed the specified Maximum
MBH Input. See “Verify Input Rate” on page 17.
2. The furnace must not operate at an airflow below the
specified Minimum Airflow CFM. On variable air volume systems it must be determined that the furnace will
not be operated if or when system cfm is reduced below
the specified minimum airflow cfm.
during off cycles. Upon a call for heat or any other time that
a prepurge cycle occurs, the air control valve will be repositioned to the maximum position for the prepurge and then
returned to the minimum position for low fire start.
Low Fire Start
The burner is controlled for proven low fire start. The actuator will position the modulating gas valve and the modulating air valve to the low fire position each time the burner is
to light off. Switch LS1 proves the air and gas valves are at
the low fire position. If LSl is not “made” at light off, the gas
valves cannot open and the flame safeguard will lock out,
requiring manual reset.
“Pilot” is Main Flame Modulated Down to Pilot Rate
3. It must be established that the gas supply is within the
proper pressure range. See “Gas Pressure Requirements”
on page 4.
The “pilot” is not a separate flame or burner. The “pilot” is
the main flame operating at its minimum rate. That minimum rate is so low that it qualifies as a pilot burner.
Start-Up Procedure
Only qualified personnel should perform the start-up and
service of this equipment. It is highly recommended that the
initial start-up and future service be performed by McQuay
certified technicians who are familiar with the hazards of
working on live equipment. A representative of the owner or
the operator of the equipment should be present during startup to receive instructions in the operation, care and adjustment of the unit.
Set Control System to Enable Heating
WARNING
Should overheating occur or the gas supply fail to shut
off, turn off the manual gas valve to the appliance before
shutting off the electrical supply.
Before Start-Up
1. Notify any inspectors or representatives that may be
required to be present during start-up of gas fuel equipment. These could include the gas utility company, city
gas inspectors, heating inspectors, etc.
2. Review the equipment and service literature and become
familiar with the location and purpose of the burner controls. Determine where the gas and power can be turned
off at the unit, and upstream of the unit.
3. Verify that power is connected to the unit and available.
4. Verify that the gas piping, meter, and service regulator
has been installed, tested, and is ready to go.
5. Verify that proper instruments will be available for the
start-up. A proper start-up requires the following: voltmeter, manometer or gauges with ranges for both manifold
pressure and inlet gas pressure, keyboard display module
or a 20K ohm/volt meter for flame safeguard signal
strength measurement, CO2 indicator, carbon monoxide
indicator, and a stopwatch for timing the gas meter.
About This Burner
Prepurge is Low-High-Low
The burner air control valve will be at the minimum position
8
To allow start-up and check-out of the burner, the control
system must be set to call for heating and must he used to
control the amount of heating. Set the control system to call
for heat so MCB-B011 energizes Relay R20. With MCBB011 closed, vary the temperature control set point to
increase, maintain, or reduce the firing rate of the burner as
required for these tests. If MCB-B09 is closed the firing rate
will decrease. If MCB-B010 is closed the firing rate will
increase. If neither are “made” the firing rate will remain
unchanged.
Start-Up Preliminary
1. Before energizing the burner verify that the modulating
air and gas valve mechanism moves freely and is not
binding, and check the linkage fasteners for tightness.
This can be accomplished without affecting any adjustments. Remove shoulder screw that connects the teflon
bushing to the actuator crank arm. The control rod can
now be manually moved back and forth, it should feel
smooth with no binding or scraping. Always remove
shoulder screw and test for binding after reinstalling the
gun assembly on Models HT050-200.
2. Close the gas line cocks. Install a Keyboard Display
Module, Honeywell Part No. S7800A1001, or connect a
20K ohm/volt meter to the test jack on the flame safeguard (Figure 7).
3. Check the burner fan wheel for binding, rubbing, or loose
set screws.
4. Check power. Position switch S3 on burner control panel
to AUTO. The LED marked POWER on the flame safeguard should come on and after a 10 second “Initiate”
period the burner motor should start. Check for (CW)
rotation as viewed through the burner fan housing inlet. If
the motor does not start, press the reset button on the
flame safeguard. If the motor still does not start, consult
the appropriate section of the “Troubleshooting Chart” on
page 22. Continue on to Item 5 when burner motor will
run 10 seconds after the switch is positioned to AUTO.
IM 685-2
5. Check voltage. With burner switch S3 at AUTO, measure
voltage across burner control box terminals 2 and NB. If
it is not between 114 and 126 volts, check the voltage and
tapping connections to the supplying transformer at the
unit main control panel.
6. Purge the gas lines. Turn off electrical power. Remove
the 1/8 inch pipe plug from the inlet pressure tap of the
first electric gas valve in the line, open the gas line cocks
upstream from there and bleed the gas line of all air.
Replace the 1/8 inch pipe plug.
7. Leak check. Using a rich soap-water mixture and a brush,
check the gas lines for leaks. Correct all leaks before
starting burner. After the burner is operating and all the
downstream valves are open, leak check that portion of
the gas train.
8. Connect a manometer to measure gas manifold pressure.
There is a 1/8 inch pipe size plugged tapping in the gas
line just before it enters the burner housing.
Preliminary “Dry” Run
1. Close the gas line cock, Remove the burner front cover
and open the control panel door. Switches LS1 and LS2
in the lower right hand corner of the control box should
be in view and the modulating actuator VM1 should be at
the minimum rate position. Verify that the right hand
switch LS1 is being held in the “made” position by the
collar on the control rod and that the switch lever is not
bottomed out against the plastic switch housing.
2. Position the burner switch S3 to AUTO. The flame safeguard will go through a 10 second “Initiate” period, after
which the burner motor will start. The modulating gas
valve actuator VM1 will drive the air valve and gas valve
to the maximum rate position. Observe the linkage for
any binding, loose fasteners, or other problems that could
have resulted from shipping.
3. When the actuator reaches the maximum rate position,
verify that the left hand switch LS2 is held in the “made”
position by the collar on the control rod and that the
switch lever is not bottomed out against the plastic switch
housing.
4. Position the burner switch S3 to OFF. Close the control
panel door and reinstall the burner front cover. Prepare to
measure the burner air box pressure by holding a rubber
manometer tube tightly over port (4) in Figure 16b. The
tube must surround the hole and seal tightly against the
burner housing to measure the static pressure through the
hole.
5. Position the burner switch S3 to AUTO and with the
burner actuator VM1 at the maximum rate position measure the burner air box pressure at port (4) in Figure 16b.
The actuator will remain at this position for the first 20
seconds of the prepurge period. Typical static pressure
readings are listed in Table 7, Column 6. Any appreciable
deviation from these values would indicate a burner air
problem that should be found before attempting to fire
the burner. These problems could include linkages disturbed during shipment, etc.
IM 685-2
Flame Start-Up
1. Open the gas line cocks and position switch S3 to AUTO.
The flame safeguard will go through the 10 second “Initiate” period, after which the burner motor will start. The
modulating air and gas valve actuator VM1 will drive the
air valve to the full open position. At full open the 60 second prepurge period will begin. After 20 seconds at maximum open, the actuator will begin a 30 second stroke to
reposition the air valve back to the minimum position.
Upon completion of the 60 second prepurge cycle, gas
valve GV1 will open (as indicated when the LED marked
PILOT comes on), the ignition transformer is powered
and the flame should come on at minimum rate.
2. Observe the gas manifold pressure manometer during this
sequence. The manifold pressure should be close to zero
(it will indicate a slight heat exchanger pressure caused
by the burner combustion air fan). When gas valve GV1
opens it should indicate a manifold pressure approximate
to the values listed in Table 7, Column 10. Approximately 3 seconds after GV1 is powered the flame will
come on and the flame signal will read 1.5 to 5.0 volts
DC. The LED marked FLAME will come on when flame
is detected and the LED marked MAIN will come on if
flame is being detected at the end of the 10 second trail
for ignition period. When the LED marked MAIN comes
on gas valves GV4-GV8 (when included) will also open
and the firing rate will be determined by the control system. On the initial start-up if the flame does not light and
the flame safeguard locks out, reset it and make several
attempts to light before assuming there are problems
other than more air in the gas lines. If initial flame operation is erratic wait until after a period of main flame operation has further purged the gas lines before trying to
“adjust out” something that may actually be caused by air
in the lines.
Modulate Firing Rates
Set the temperature control system so the burner actuator
VM1 will modulate to increase the firing rate. Observe the
flame signal and the manifold pressure manometer as this is
occurring. The flame signal should remain between 1.5 to
5.0 volts DC through the entire range of the burner, and the
manifold pressure should be between the values indicated by
Table 7, Column 9 and 10. If the manifold pressure shoots
above these values and then slowly returns to normal as the
burner is modulating down to a lower firing rate, isolate
which combination gas control is causing this. Check that
valves pressure regulator adjustment per “Gas Valve Pressure Regulator Adjustment” section. If this condition cannot
be adjusted out, replace the valve. If combustion appears
normal, proceed with the combustion test.
9
Combustion Tests
These tests should be run when the furnace is at normal operating temperature (after the furnace has been running 10 to 15
minutes), and should be run at several firing rates including
maximum and minimum.
Cycle the Unit
Cycle the unit through several start-ups with the temperature
controls calling for first minimum rates and finally maximum rates. Be alert for any hints of trouble or unexplained
inconsistencies that could indicate future problems.
a. Check input: See Verify Input Rate
Record Data
After the gas burner has been successfully started up, checked
out and is operating correctly, readings should be taken and
recorded for future reference (see Table 8). If problems
develop in the future, variations in these readings will indicate what has changed and where to start looking for problems.
b. Check CO2: See Check CO2, CO & Stack Temperature
c. Check CO: See Check CO2, CO & Stack Temperature
Figure 6a. Typical Electrical Schematic with RM7897A
10
IM 685-2
Typical Sequence of Operation
When the rooftop unit is energized 120 volt power is supplied to the system on/off switch (S1), to burner on/off
switch (S3) and 24 volts to the (BO#11) contacts on the main
control board (MCB).
Note: On field supplied controls, 120V power is supplied
through the system on/off switch (S1) to burner on/off
switch (S3) and to the field supplied gas heat on/off
contacts.
Burner on/off switch (S3) will power the modulating gas
valve actuator (VM1) and terminal #5 (L1) on the flame
safeguard (FSG). Upon a call for heat, the control system
will close (BO#11) on the main control board (MCB), thus
energizing relay (R20). When 120V power is furnished
through the system on/off switch (S1), through the burner
on/off switch (S3), through relay (R20) contacts, through the
high limit control (FLC) and through the optional automatic
reset low gas pressure switch (LP5) and the optional manual
reset high gas pressure switch (HP5), terminal #6 on the
flame safeguard (FSG) is powered. The flame safeguard then
energizes its terminal #4, which powers the burner combustion air blower motor (BM). Whenever power is restored to
the flame safeguard, the flame safeguard will go through a
10 second initiation period before the prepurge period will
begin.
The burner air control valve will be at minimum position
during off cycles. Upon a call for heat or any other time that
a prepurge cycle occurs the air control valve will be re-positioned to the maximum position for the prepurge and then
returned to the minimum position for low fire start.
(VM1), through the N/C contacts of (R20) and (R23), positions the burner air and gas control valves to minimum after
run cycle. When (R20) is energized for a new call for heat,
(VM1) through the N/O contacts of (R20) and the N/C contacts of (R21), will re-position the burner air valve to its
maximum open position for pre-purge. When the air control
valve reaches the full open position switch (LS2) is 'made',
powering (FSG) terminal #7 through the burner air switch
(AS). This initiates the 60 second prepurge cycle. Concurrently, (LS2) powers timer (TD10) which will energize relay
(R21) after 20 seconds. When (R21) is energized (VM1) will
start the air control valve on its way toward the minimum air
valve position through the N/O contact of (R21) and the N/C
contact of (R23). At the completion of the 60 second
prepurge cycle the valve will be at the minimum open position and the minimum position switch (LS1) will be
“MADE”. If (LS1) is not “MADE” the combination gas control start valves (GV1) will not open and the burner will go
out on safety lockout.
After completion of the 60 second prepurge period there will
be a 10 second trial for ignition during which terminal #8
(combination gas valve - GV1) and terminal #10 (ignition
transformer - IT) will be energized. If flame is being
detected through the flame rod (FD) at the completion of the
10 second trial for ignition period terminal #10 (ignition
transformer - IT) will be de-energized and terminal #9 (relay
R23 coil and main gas valves - GV4 and GV5) will be energized and the control system will be allowed to control the
firing rate. The flame safeguard contains 'LEDS' (lower left
corner) that will glow to indicated operation.
After the flame has lit and been proven, relay (R23) is energized allowing (VM1), as controlled by (BO#9) and
(BO#10) on the main control board (MCB) to position the
burner air and gas valves for the required firing rate. When
the main control system closes (BO#10) the gas valve actuator will re-position toward a higher firing rate until (BO#10)
opens or the actuator reaches its maximum position. When
the main control system closes (BO#9), the actuator will reposition toward a lower firing rate. If neither (BO#9) or
(BO#10) on the main control board (MCB) are closed, the
actuator will remain at its present position. The heating
capacity is monitored by the main control board (MCB)
through (AI #10) via a position feedback potentiometer on
the actuator.
In the event the flame fails to ignite or the flame safeguard
fails to detect its flame within 10 seconds, terminals #4, 8, 9,
and 10 will be de-energized, thus de-energizing the burner
and terminal #3 will become energized. The flame safeguard would then be on safety lockout and would require
manual resetting. Terminal #3 will energize the heat alarm
relay (R24), which would then energize the remote 'HEAT
FAIL' indicator light and send a fail signal to binary input #5
in MicroTech II main control board (MCB).
If an attempt is made to restart the burner by resetting the
flame safeguard, or if an automatic restart is initiated after
flame failure the earlier described prepurge cycle with the
wide open air valve will be repeated.
If the unit overheats, the high limit control (FLC) will cycle
the burner, limiting furnace temperature to the limit control
set point.
Figure 6b. Typical Piping Schematic
TEST
CONN.
v
VENT TO
(OPT.)
ATMOSPHERE VENT
VENT
VENT
CAPPED LEAK
(OPT.)
(OPT.)
TEST COCK (OPT.)
(OPT.)
LP5
HP5
(OPT.)
GV2
GV3
COMBINATION GAS CONTROLS
LO PRESS.
HI PRESS.
HIGH PRESS. SHUTOFF
SAFETY
SAFETY
TEST
SWITCH
GV1B GV1A
SWITCH
REG.
VALVE
VALVE
COCK
COCK
V
MODULATING
ACTUATOR
AIR
SWITCH
IM 685-2
BURNER
BLOWER
GV4B
GV4A
GV5B
GV5A
(OPT.)
N.O. VENT
VALVE
(REQ'D FOR
OVER .50 PSI)
GV1 - HT 020 TO 200
GV4 - HT 040 TO 200
GV5 - HT 079 TO 200
GV6 - HT 110 TO 200
GV7 - HT 140 TO 200
GV8 - HT 200 ONLY
11
Flame Safeguard
See manufacturer's bulletin for more detailed information on
flame safeguard RM7897A.
The Honeywell RM7897A is a microprocessor based integrated burner control that will perform self-diagnostics, troubleshooting, and status indication, as well as the burner
sequencing and flame supervision.
Keyboard Display Module
The Honeywell S7800A1001 module is an optional device
available for use with the RM7897A. It can be a permanent
accessory added to the RM7897A or it can be carried by the
service technician as a tool that is very easy to mount when
servicing the RM7897A. It mounts directly onto the
RM7897A and has a 2 row by 20 column display. The module
will indicate flame signal dc volts, sequence status, sequence
time, hold status, lockout/alarm status, total hours of operation, total cycles of operation, and can provide 127 different
diagnostic messages for troubleshooting the system.
The module will give a fault history. It can be mounted to the
RM7897A and will retrieve information on the six most
recent faults.
Operation
Initiate Period: When the relay module is powered it goes
through a 10 second “Initiate” period. It will also enter into
the “Initiate” period if electrical power problems such as low
voltage or momentary interruption occur while the unit is
operating. Operation of the burner fan motor is delayed
throughout the “Initiate” period.
Standby: After the initiate period is completed the module
will enter the standby mode and await a call for heat by the
temperature control system.
Normal Start-Up:
Prepurge: Upon a call for heat the prepurge period will
begin. If the air switch does not detect fan operation in the
first 10 seconds into the prepurge period a recycle to the
beginning of the prepurge will occur.
Ignition Trial: The “start” combination gas control and the
ignition transformer are powered for 10 seconds following
the prepurge. Flame must be proven at the end of that 10 second period or safety shutdown will occur.
Consult the Honeywell bulletin 65-0090-1 “7800 Series,
Keyboard Display Module” and 65-0118-1 “7800 Series,
System Annunciation, Diagnostics and Troubleshooting.”
Run: If flame is proven at the end of the 10 second ignition
trial the “start” combination gas control will remain powered
and on multiple valve units, the other parallel piped main
valves will become powered. If a flameout occurs the module will recycle within 3 seconds, and initiate a new prepurge
period. If flame continues to be detected the module will be
in Run until the power is interrupted to terminal 6 indicating
that the temperature control system no longer requires heat,
or that the high limit or another safety control has opened.
Figure 6c. Typical Burner Control Box
Figure 7. RM7897A Flame Safeguard
NB NB
1
2
3
1
2
3
4
C1
5
6
4
C1
5
6
C2
C2
AIR
SW.
LS2
C
12
NC
NC
NO
NO
LS1
C
C
IM 685-2
Service
General
Before starting service on this burner take the time to read
the sections “About This Burner” on page 8 and “Typical
Sequence of Operation” on page 11 to get an overview.
Gun Assembly
The McQuay gas burner gun assembly is easily removable
and includes the ignition electrode assembly, the flame rod
assembly, and a “Base Air” fitting with orifice. The positioning of this assembly is not considered field adjustable. When
positioned correctly the gun disc will be perpendicular to the
blast tube and back in the cylindrical portion of the blast tube
as shown in Figure 8. The gun pipe will be concentric with
the blast tube.
shoulder screw (12), Figure 16a, and manually slide the control rod back and forth to test for binding after reinstalling
the gun assembly on Models HT050-200. Do not operate the
burner without a tight seal at the grommet.
Flame Rod Adjustment
The gun assembly is removed for flame rod inspection or
service. When correctly adjusted the flame rod insulator will
be concentric with the hole it passes through, not be shorted
out against the disc, the 0.75 inch long end tip will point
toward the 0.086 inch diameter alignment hole, and the end
tip will clear the disc according to dimension “C” in Figure
9.
C
FLAME ROD
ALIGN FLAME ROD TIP
WITH .086 DIA HOLE
.086 DIA.
IN BURNER DISC.
HOLE (REF.)
Figure 8. Gun Assembly
BASIC AIR
ORIFICE
A
B
IGNITION
ELECTRODE
.086 DIA. HOLE
(REF.)
ALIGN IGNITION
ELECTRODE TIP
WITH .086 DIA HOLE
IN BURNER DISC.
.09
Figure 9. Flame Rod and Ignition Electrode
Model HT***
A
B
020
025
032
040
050
064
065
079
080
100
110
140
150
200
1.98
2.04
2.04
2.17
2.17
217
2.17
2.07
2.07
2.30
2.24
2.30
4.13
4.13
1.94
1.88
1.88
1.75
1.75
1.75
1.75
1.85
1.85
1.62
1.68
1 62
1.62
1.62
Base Air
Orifice I.D.
.060
.060
.067
.070
.089
.089
.089
.102
.102
.102
.098
.110
.110
.110
Gun Assembly Removal and Installation
Unplug the ignition lead from the ignition electrode and
unplug the flame rod lead from the flame rod. Disconnect the
3/8 inch copper tube at the brass fitting on the left side of the
gun pipe, open the pipe union and remove the gun assembly.
Models 050-200 include an air tube that must be lifted up
and out of the grommeted hole it is nested into as the gun
assembly is removed. The gun assembly may have to be
manipulated and wiggled as the disc is withdrawn back
through the blast tube. Reassemble in reverse order, being
particularly careful to correctly reinsert the air tube into the
grommeted hole. The tube should slip into the grommet so
there is little leakage, but it should not bear down on it or it
can cause binding on the sliding air valve. Always remove
IM 685-2
Model HT***
020
025
032
040
050
064
065
079
080
100
110
140
150
200
C
.09
.09
.09
.09
.40
.40
.40
.40
.40
.44
.35
.35
.48
.75
Flame Rod Installation
The flame rod must be disassembled from its porcelain insulator for removal or installation. Remove the two nuts on the
threaded end of the flame rod, pull the rod out of the insulator, and then remove the insulator by loosening its clamp
screw.
Ignition Electrode Adjustment
The gun assembly is removed for ignition electrode inspection
or service. When correctly adjusted the ignition electrode
insulator will he concentric with the hole it passes through, the
end of the insulator will be flush with the outside surface of
the gun disc, the electrode tip will point toward the 0.086 inch
diameter alignment hole, and there will be a 0.09 inch spark
gap to the gun disc (see Figure 9). The ignition electrode can
he removed by loosening the clamp screw and sliding the
entire assembly through the disc hole.
13
Air and Gas Adjustments
The burner has been adjusted and tested at the factory with
accurate instruments. There should not be a need to readjust
the burner after the unit has been installed.
Verify that the gas supply pressure is correct, the electrical
power is correct, and test the burner thoroughly. Do no make
adjustments unless there is a clear indication that there is a
problem, and proper instruments are available so the adjustments can be made correctly.
Gas Supply Pressure
The maximum pressure rating of the combination gas control(s) used on this burner is 0.50 psi (13.9 in. w.c.), as measured at (2), Figure 16a. If the gas supply pressure is higher
than this an additional regulator must be installed so the
pressure will not exceed 0.50 psi.
Many gas burner problems are due to gas supply pressure
problems. High or low gas pressures can cause nuisance
lockouts of the flame safeguard and combustion problems.
Low gas pressure will reduce the heat output of the furnace,
and if extreme, can cause combustion problems and flame
safeguard lockouts. Every gas supply system has a high pressure regulator somewhere upstream. Perhaps it is at the
meter and adjusting the outlet pressure is not an option, the
following discussion on the “High Pressure Regulator”
would still apply.
High Pressure Regulator
If a high pressure regulator is included as part of the burner
gas train or is included elsewhere in the gas supply line, it
should be adjusted so the pressure at the inlet tap to the combination gas valves is 7.0 in. w.c. The inlet tap is (2) on Figure 16a. Check that the pressure is relatively consistent as
the firing rate changes. If any other equipment is served by
that same gas line or pressure regulator, check that the gas
pressure also remains relatively consistent when that equipment is turned on and off. Verify that the regulator closes off
tightly at zero flow by observing that the pressure does not
creep up when the unit is off. If it does, excessive pressure
will have built up over the off period, possibly exceeding the
pressure rating of the combination gas controls, and causing
other problems at light off.
Gas Adjustments
See the sections on “Gas Valve Pressure Regulator Adjustment,” “Gas Supply Pressure,” and “High Pressure Regulator.” The gas flow rate is determined by the gas pressure and
a characterized element within the modulating gas valve.
The stem of the valve connects to the bracket that positions it
with lock nuts that are adjusted at the factory and determine
the minimum firing rate of the burner. Other than gas pressure adjustments, this is the only adjustable control of the
gas. Adjusting the minimum rate is not intended to be a routine field adjustment. Properly adjusting the minimum rate
requires clocking a gas meter at very low flow rates, or connecting a test flow meter into the gas train.
14
Air Adjustments
Airflow and the resultant combustion characteristics have
been preset and tested at the factory and no further adjustments should be required. Airflow to the burner is determined by the characterized plate on the air valve outlet (1)
and an adjustable plate (2) on Figure l0. The adjustable plate
can increase or decrease airflow across the entire stroke of
the valve. If burner airflow is in question, measure the static
pressure at Ports (4) and (5) in Figure 16a and 16b, and compare those readings with Columns 6 and 8 in Table 7. A significant difference should be checked out.
Air and Gas Control Linkage
An L-shaped control rod is connected to the actuator and
passes through the burner housing and into the control box.
This control rod positions the valves that control the burner
air and gas, and actuates switches in the control box to prove
when it is at the maximum and minimum position. When the
actuator positions the control rod to the minimum rate position, the bracket on that rod that connects to the air valve and
gas valve should be firmly bottomed against the end of the
gas valve which acts as its stop. The linkages to the air and
gas valve should be straight and in alignment. Although the
bracket is to bottom out, the plate connected to it which
slides from right to left to control airflow should slide freely
and not be forced against either the right or left side member
of the air box.
At the minimum rate position maintain a gap according to
dimension “D” in Figure 10. With that sliding plate in this
minimum rate position, check dimension “E” in Figure 10.
To gauge opening “E,” use a drill blank held perpendicular
to the plate. For Models 050-200 opening “E” can be
accessed through the grommeted opening in the primary air
collector. See (3), Figure 10, for Models 020-040 the primary air collector must be removed. Generally, it is easier to
remove the collector with the inch diameter tube still
attached by disconnecting the tube at the other end.
At the maximum rate position the sliding blade should be
full open, but it should not be forced against the left side
piece of the air box.
The control rod bracket that connects the air and gas valves
must be correctly positioned on the control rod such that the
bracket will be firmly held under tension against its stop
when the actuator is in the minimum rate position, and so the
sliding blade will open fully without making contact at the
end of the stroke. When modulating towards the minimum
rate position the actuator will continue to travel after the
bracket contacts the stop, flexing the vertical end of the control rod so the bracket is held under tension. To correctly
locate the bracket on the rod, first adjust the air damper linkage so there will be a gap per dimension “D” in Figure 10,
when the bracket is bottomed out against the end of the
valve. Second, loosen both set screws on the bracket assembly so the bracket is free to slide on the rod. Third, position
the actuator to the maximum rate position. Position the sliding blade to the wide open position.
IM 685-2
Grasp the rod and while applying some thrust to the rod in
the direction of the actuator to take up any free play, and
with the bracket in alignment with the linkages that connect
to it, tighten the two set screws. Return the actuator to the
minimum rate position.
The adjustable plate (2) in Figure 10 is positioned to provide
an opening per dimension “F.”
Figure 10. Air and Gas Control Linkage
PRIMARY AIR
COLLECTOR
PROFILE
PLATE
ƒ

ADJUSTABLE
PLATE
‚
E
D
F
10º
MIN
RATE
G
IM 685-2
Switch Adjustment
Switches LS1 and LS2 prove maximum and minimum position of the control rod. These switches are located in the control box switch compartment and have a limited range of
adjustment. When the two nuts that secure the switches are
loosened the switch will pivot on the inner stud and the outer
stud can be moved up and down. The switches should be
adjusted such that when the collar mounted on the actuator
rod is moved into position and pushes in the lever on the
switch, the switch will click to the “made” position, but the
lever will not bottom out against the switch body. When
properly adjusted the lever can move an additional 0.02
inches, as proven by slipping a feeler gauge between the
switch lever and the collar when in the “made” position. The
collar on the control rod should be adjusted so the switch
lever it is actuating will rest squarely on the outer surface of
the collar but only 0.03 inches from the edge. If the collar is
located for an engagement that is longer than 0.03 inches,
the collar may not reach the actuator on the other switch
when at the other end of its stroke.
Altitude Considerations
For altitudes of 2000 feet and higher, the gas burner must be
derated 4% for every 1000 feet of altitude.
90º
Model
HT***
020
025
032
040
050
064
065
079
080
100
110
140
150
200
Actuator Crankarm
The actuator crankarm should not require adjustment. The
radius indicated by “G” dimension in Figure 10, will result in
a complete stroke from minimum to maximum, and provide
the correct amount of over travel to bottom out the linkage
bracket at the minimum rate position. Do not attempt to modify firing rates, etc. by changing the radius of the crackarm.
Example: An 800 MBh output furnace at an altitude of 3000
feet is derated (0.04 x 3 = 0.12). At 1000 MBh input (1000 x
0.12 = 120 MBh), the actual input is (1000 - 120 = 880 MBh)
at 3000 feet.
D
E
F
G
.005
.005
.005
.005
.020
.020
.020
.020
.020
.020
.020
.020
.020
.020
.116
.125
.101
.101
.099
.136
.136
.106
.106
.110
.136
.136
.140
.140
.50
.83
.82
1.25
1.25
1.60
1.60
1.88
1.88
2.44
1.05
3.30
3.30
4.40
3.30
3.30
3.30
3.30
3.30
3.30
3.30
3.30
3.30
3.30
4.28
4.28
4.28
4.28
The method of derating the burner is to reduce the manifold
pressure for the pilot and main burner. First, refer to Table 7.
Multiply the Gas Manifold Orifice Pressure (at max. rate)
shown under Column 9, by the following altitude factors:
2000 feet = 0.845
5000 feet = 0.640
3000 feet = 0.774
6000 feet = 0.578
4000 feet = 0.706
7000 feet = 0.518
15
Gas Valve Pressure Regulator Adjustment
The high turndown burner uses combination gas controls to
provide redundant on-off gas control and pressure regulation.
A burner will have from one to six of these controls piped in
parallel depending on the BTU rating of the burner. When
two or more valves are in parallel their pressure regulators
must be adjusted so the valves maintain the specified manifold pressure and are balanced so each valve handles its share
of the load. To determine that the valves are balanced, the
manifold pressure must be measured and adjustments made
at both maximum and minimum capacity. As the burner modulates from maximum capacity down to minimum capacity it
is normal for the manifold pressure to rise. This is because
the pressure loss through the valve and fittings is being
reduced as the flow rate is reduced. If one (or more) valve is
not in balance with the others, the pressure at the minimum
rate will rise higher than normal.
While the burner is operating and only one combination gas
control is open, increase the firing rate of the burner. As the
firing rate is increased the manifold pressure will be relatively constant until the gas flow rate exceeds the capacity of
that single valve and the manifold pressure starts to drop off.
The pressure adjustments should be made at the maximum
gas flow rate just before the manifold pressure starts to drop
off, and the following should be considered:
Clockwise rotation of the pressure adjusting screw on the
combination gas controls will increase the pressure set point,
and counter-clockwise rotation will reduce the pressure set
point (see Figure 11).
c. If the regulator cannot be adjusted up to the required set
point, or if that set point seems to be the highest pressure
the regulator can be adjusted to, the flow rate used for this
procedure is too high and must be reduced by repositioning the actuator to a lower firing rate, or the gas supply
line pressure is too low.
Figure 11. Combination Gas Controls
INLET
PRESSURE
TAP
PRESSURE REGULATOR ADJUSTMENT
(UNDER CAP SCREW)
OUTLET
INLET
GAS
CONTROL
KNOB
ON
OFF
(SHOWN AT "ON")
OUTLET
PRESSURE
TAP
Adjustment Procedure for Parallel Valves
When a manifold pressure adjustment is required, the first
step is to adjust the pressure regulator of each combination
gas control to the minimum rate manifold pressure (Table 7,
Column 10) while only that valve is operational, and it is
handling approximately its normal maximum rate CFH of
gas. The manual shutoff valve knobs are used to control gas
flow so just one valve is operating at a time.
To determine a firing rate suitable for this adjustment, first
modulate the burner down to the minimum rate. At this flow
rate only the valve with the highest pressure regulator set
point will be operational, the other valves will be shut down
by their integral pressure regulators because the manifold
pressure is slightly higher than their set point. While the
burner is operating at that minimum firing rate slowly close
all but one of the manual shutoff valve knobs on the combination gas controls. With care this can be done without the
burner loosing flame and shutting down. Watch the manifold
pressure manometer as each valve is being closed. If the
manifold pressure starts to drop rapidly in response to the
knob movement, it indicates this combination gas control has
the higher pressure adjustment and is supplying the gas to the
manifold. Leave this valve open, and continue closing the
remaining valves until only that one valve is open, and then
adjust that combination gas control first.
16
a. The manifold pressure does not always immediately
respond to regulator adjustments. Wait a few seconds after
making an adjuster movement for the regulator to respond
and equalize.
b. When making an adjustment rotate the adjuster CCW
until the manifold pressure is below the desired set point,
and then slowly rotate the adjuster CW and nudge the
pressure up to the desired set point.
After adjusting valve 1, open valve 2. If opening the additional valve does not cause the manifold pressure to go up,
increase the pressure regulator setting of valve 2 until an
increase is observed, this would indicate that the valve has
started functioning. Then slowly close the first valve. Proceed to adjust valve 2. Repeat this procedure until all valves
have been adjusted.
Open the manual shut off knobs on all the combination gas
controls and modulate the burner up to the maximum firing
rate. The resulting manifold pressure should be close to the
Maximum Rate Manifold Pressure indicated in Table 7, Column 6. If further adjustment is required it should not be necessary to go through the entire procedure again. If the
manifold pressure is to be increased, make small but equal
(about 1/4 revolution) CW rotations of the pressure adjusting
screw on every combination gas control and check the resulting manifold pressure, both at maximum and minimum rate.
Check Manifold Pressure at Minimum Rate
When several combination gas controls are in parallel and are
handling a low flow rate, the combination gas control with
the highest set point is essentially handling all the gas.
Observe the gas manifold pressure at the minimum rate. If it
is higher than the pressure specified under Column 10 in
Table 7, locate and adjust the dominant combination gas control. Test each combination gas control by slowly manipulating the manual shutoff knob toward the closed position while
observing the manifold pressure. The pressure will only
respond to movement of the knob on the dominant valve. The
manifold pressure will drop as the gas flow is throttled back,
using the knob on the combination gas control to partially
close that manual valve.
IM 685-2
Generally a valve will he found that has an effect, and very
little adjustment will cause a reduction in the minimum rate
manifold pressure. Reduce the pressure adjustment of that
dominant valve by slowly rotating the adjuster CCW until
the manifold pressure no longer drops in response to that
adjuster movement. If the manifold pressure is still high after
that first adjustment, another valve may have become the
dominant valve and that may also have to be isolated and
adjusted to get down to the specified minimum rate manifold
pressure. After making this type of adjustment it is necessary
to recheck the maximum firing rate manifold pressure and
perhaps readjust it, making very small but equal adjuster
movements on each valve.
Combustion Testing
Proper start-up and maintenance requires periodic combustion tests and the systematic recording of those test results
for future reference. Before making combustion air adjustments, check for proper input rate.
Verify Input Rate
To determine the input rate it is necessary to know the BTU
per cubic foot of gas being used. If this is not known, contact
the gas supplier. Check input rate by timing the gas meter
dial with all other appliances and their pilot lights off.
To verify the input rate using the gas meter, use a stopwatch
and time one revolution of the dial. Calculate the input with
the following formula:
MBH Input= A x B x 3.6
C
Where: A = BTU/cu. ft. of gas
Typical: Natural gas= 1000, LP gas=2500
B = Cu. ft. per revolution of meter dial
C = Seconds required for 1 revolution of meter dial
Check CO2, CO & Stack Temperature
Flue gas samples are to be taken from inside one of the secondary tubes. If the sample is taken from the flue box rather
than the tube, the sample will be diluted with outside air and
lower readings will result. If flue gas temperature is to be
measured, this must be done in the flue box, not in the tube.
The temperature gradient within the tubes would cause high
readings near the center of the tube and low readings near
the edge. Temperatures should be measured within the flue
box where a good mix will be present. The flue box includes
two 5/16" holes for test purposes. One hole lines up with the
end of a secondary tube for taking flue gas samples. The
other hole, through the side of the flue box, is for thermometer insertion.
If the CO2 and/or CO readings are not within the range indicated, see “Troubleshooting Chart” on page 22.
Figure 12: Checking Temperature
300º
400º
500º
Measure
Temperature
600º
Temperature Gradient
within Tube
Co2
Sample
Typical Readings:
CO2
9½ to 10½ percent at maximum rate
4 to 7 percent at minimum rate
CO
.005 percent (50 PPM) or less
Cleaning Heat Exchangers
Models 032 thru 200 (see Figure 13)
1. Remove the flue box front wrap (1) and the rear inspection cover (3).
2. Remove and clean the turbulator (2)‚ from each tube and
clean the flue box.
3. Clean each tube with a 2½" round flue brush.
4. Remove the brushings and if required clean the combustion
chamber and header through the rear inspection door port.
5. Reinstall the inspection door (3). Snug the screws but do
not overtighten and crush the insulation.
6. Reinstall a turbulator (2) in each tube approximately
flush with the tube ends. The end of the turbulators are
formed such that the end will bind within the tube end
and lock the turbulator in place.
7. Reinstall flue box front wrap (1).
Figure 13. Models 032 thru 200 Heat Exchanger
1
2 1/2 Round Flue Brush With 7 Foot Handle
3
2
Condensate Drain
IM 685-2
17
Models 020 thru 025 (see Figure 14)
1. To gain access to the inside of the combustion chamber,
detach the burner from the furnace and set it on the floor
of the vestibule (see Figure 14, Item (3)). The burner is
attached to the furnace studs with four nuts. Conduit
lengths allows this movement of the burner without disconnecting wiring. The union on the gas line must be
opened.
2. Remove the flue box front wrap (1).
3. Remove and clean the turbulator (2) from each tube and
clean the flue box.
4. Clean each tube with a 2½" round flue brush.
5. Remove the brushings and if required clean the combustion chamber and header through the burner mounting
tube.
6. Reinstall the burner.
7. Reinstall a turbulator in each tube approximately flush
with the tube end, locking them in place with the wedge
clips on each turbulator.
8. Reinstall flue box front wrap (1).
Figure 14. Models 020 thru 025 Heat Exchanger
2 1/2 Round Flue Brush With 4 Foot Handle
1
Wind Deflector
3
2
Condensate Drain
Leakage Symptoms
1. Odor - Odors in the building are usually being brought in
through the outdoor air intakes and do not indicate leakage from the furnace. Check for down draft conditions
and check the location of the flue exhausts of other equipment that may be pulled into the outdoor air intake. A
major and obvious furnace rupture can be a source of
odor. In general, small leaks in a furnace will not be a
source of odor or danger because the pressure created by
the supply fan is greater than the pressure inside the furnace. Therefore when the supply fan is operating, leakage
will be into the furnace, not out of the furnace and into
the air stream. If the control system is such that the furnace comes on and warms up the heat exchanger before
the supply air fan comes on, and there is odor when the
supply fan first comes on, this could be caused by leakage. During the time the furnace is on and the supply fan
is off the leakage would be out off the furnace and then
when the supply fan came on it would blow those products of combustion into the supply duct.
18
2. Low CO2 Readings - Low CO2 readings that cannot be
corrected can be caused by air leaking into the heat
exchanger and diluting the flue gas. If this is suspected,
take two consecutive CO2 readings, one with the supply
fan running and one with the supply fan off. If the CO 2
increases with the supply fan off, it could indicate leakage. Note that CO2 samples must be taken from inside a
tube, not just from inside the flue box.
Checking for Leaks
1. Open up the rear casing panel while the unit is shut off
and visually inspect the heat exchanger.
2. Visually inspect the heat exchanger while the burner is
operating, looking for light coming through holes. The
burner should only be operated for a few minutes with the
supply fan off, and take necessary safety precautions
around the hot heat exchanger.
3. Perform consecutive CO2 tests with supply fan off and
on. See Item 2 under “Leakage Symptoms.”
4. Smoke Bomb Test - Cover the flue box openings, open
the rear casing panel so the heat exchanger is accessible,
toss a smoke bomb into the heat exchanger through the
rear inspection port, replace the port cover, and with a
bright light look for smoke leaking through the heat
exchanger. Remove the remains of the smoke bomb and
uncover the flue box openings before attempting to operate the furnace.
Note: In most cases small leaks in the heat exchanger are not
a source of danger. Because the pressure created by the supply fan is greater than that inside the heat exchanger, the
leakage will be into the heat exchanger, not out of the heat
exchanger and into the airstream.
Causes of Failures
1. Improper Application - The furnace rating plate specifies a “Minimum Airflow CFM.” The furnace must not be
operated when airflow is below this minimum cfm. If the
furnace is being used on a variable air volume system, the
control system must be such that the furnace will not
operate when the supply fan cfm has fallen below this
minimum specified cfm. The furnace rating plate also
specifies a “Maximum MBH Input” which must not be
exceeded. See “Verify Input Rate” on page 17.
2. Control Failure - The limit control does not function
properly to shut off the burner when the heat exchanger
temperature becomes excessive. In most situations, a
properly controlled unit will never even require the limit
control to shut off the unit. The limit control should be a
backup control and a problem attributed to a limit failure
would generally indicate a control problem in addition to
the limit failure.
IM 685-2
3. Excessive Condensation - Applications which will produce condensation require an all stainless steel heat
exchanger that is resistant to the effects of this condensation and that will give long heat exchanger life. The likelihood of condensation increases with:
a. Colder supply air temperature across the secondary
tubes, as on units taking in a lot of outdoor air in
colder weather.
b. Lower heat flow through the secondary tubes, as on
modulating burners when operating at reduced input.
c. High airflow across the secondary tubes such as any
application with a low temperature rise furnace.
4. Chemical Deterioration - Refrigerant leaks, some aerosol can propellants, fumes from dry cleaning establishments, beauty shops, swimming pools, and others, often
have detrimental effects on heat exchangers when they
get into the combustion air supply and thereby into the
combustion. Even fumes from nearby roof exhaust fans
can cause problems.
5. Inadequate or Distorted Airflow - Internal baffles that
have been repositioned or have loosened up and moved
can distort the airflow and cause failures. Construction
rubbish, shipping cartons, and insulation that has come
loose will occasionally end up inside a unit and block airflow to part of the furnace, resulting in a failure. These
items can also alter the air or heat flow to the fan limit or
some other control and contribute to a failure.
Replacing Heat Exchanger
1. Remove the complete flue box, the casing panel through
which the flue tubes pass, and the rear inspection cover.
Open the hinged rear door.
2. The burner is mounted on and supported by the heat
exchanger studs with four nuts. When removing the heat
exchanger, the burner must either be removed or blocked
in place. Remove the four burner mounting nuts and the
two exchanger bolts located 2" above the upper burner
mounting nuts.
3. When it is necessary to remove any air baffles surrounding the heat exchanger, carefully note the locations and
clearances of these baffles before removing them so they
can be replaced in the exact same position.
A modulating burner will produce more condensate than an
on-off burner. As the firing rate of the burner is reduced the
flue gas temperature will he reduced, and if it is reduced
below its dew point condensate will be produced.
A furnace that is heating a high percentage of outside air will
also produce more condensate. The colder the air contacting
the heat exchanger, the lower the resulting flue gas temperature, and consequently the more condensate.
Do not think a furnace has a problem because it produces
condensate anymore than you would think a cooling coil has
a problem because it produces condensate. However suitable
steps should be taken to manage the flow of the condensate
produced.
Most condensate will be produced in the secondary tubes
where flue gas will sweep it into the flue box. Condensate
will also come from the combustion chamber. Models 020
and 025 have a piped combustion chamber condensate drain,
and Models 032 through 200 have a rear cleanout port with
an integral condensate drain.
Condensate will also drip from the drains in the two outer
corners of the flue box, and from the drip shield below the
rear cleanout port. Condensate should not be running down
the unit, except at times the wind may blow the dripping condensate mentioned above. The drip shield below the rear
cleanout port must be correctly installed as shown in the following section.
Rear Inspection Cover (see Figure 15)
The rear inspection cover is equipped with a stainless steel
drip shield to keep condensate away from the side of the unit
if condensate drips out of the inspection cover. The shield (1)
must fit snugly against the bottom of the cleanout port tube
(2) at (3) so condensate (4) cannot run back along the underside of the tube and into the unit or down the side of the rear
panel.
Note: If an excessive amount of condensate is dripping
out of the rear inspection cover, check the condensate drain for blockage and clean if necessary.
Check the Rear Condensate Drain annually for
blockage.
Figure 15. Inspection Cover (Models 032 thru 200)
2
4. Remove the two bottom bolts at the back of the heat
exchanger.
3
5. Withdraw the heat exchanger through the back of the casing.
Furnace Condensation
A furnace will produce condensation when the flue gas temperature falls below its dew point temperature. A more efficient furnace will transfer more of its heat into the building,
and leave less heat in the flue gas. This results in a lower flue
gas temperature and more condensate.
IM 685-2
1
2
4
1
3
19
Combination Fan And Limit Control
The fan limit control is a hydraulic action type with a remote
sensing element and connecting capillary tube. The sensing
element is locked into a bracket located on one of the heat
exchanger tubes about halfway toward the back of the furnace, on the side away from the blower. One corner of the
bracket is bent aside to remove the element.
Yearly
1. Gas Train - Check all valves, piping, and connections for
leakage. Remove burner gun assembly. Inspect, and if
required, clean the flame rod, ignition electrode, main
burner disc, and blast tube. Check tightness of linkage fasteners and bolts that could work loose from vibration and
movement.
Normal setting of the FAN control: Fan On=125°F, Fan
Off=100°F.
2. Combustion - Check quality of combustion. Test CO2 and
CO and look for irregularities in fire shape. If combustion
characteristics have changed since the last test, determine
the cause. Changes in input, changes in the BTU content
of gas being supplied, reduced combustion air due to dirty
blower wheel, or flue passages in need of cleaning can all
cause changes in CO 2 reading. When a readjustment
seems necessary, do not make the adjustment without first
trying to determine if the required change is not an indication that something else is in need of correction.
The LIMIT control must never be set higher than the temperature listed below. If the burner is shutting off on high limit at
these settings, it indicates that there is a problem with the furnace not getting enough air or it is being overfired.
Table 4. LIMIT control set points
BURNER MODEL LIMIT CONTROL BURNER MODEL LIMIT CONTROL
SET POINT
SET POINT
020
215
079
181
025
160
080
229
032
196
100
170
040
154
110
222
050
229
140
168
064
185
150
194
065
232
200
151
Maintenance
Preventative maintenance is the best way to avoid unnecessary expense and inconvenience. The system should be
inspected at regular intervals by a qualified service technician. The service intervals below are typical for average situations but will have to be adjusted to suit the particular
circumstances.
Fuel pressure settings, control settings, and linkage adjustments should only be made by persons thoroughly experienced with the burner and control system and should not be
tampered with by persons without such experience.
Always replace covers on burner controls and boxes as the
electrical contacts are sensitive to dust and dirt. Maintenance
of flame safeguard, controls, gas valves, and other such components should be performed in accordance with instructions
contained in the manufacturer's bulletins.
Monthly
1. Check air filters and main supply fan drives, replacing if
required.
2. Check flame signal with a keyboard display module or a
DC voltmeter.
Twice Yearly
1. Burner Air - Check burner fan wheel for dirt build-up
and lint. Check combustion air intake louver and flue box
for dirt buildup and accumulation of wind borne debris.
2. Cleaning - Inspect flue tubes and combustion chamber,
cleaning as required. Keep burner vestibule clean. Dirt
and debris can result in burner air blockages.
20
3. Flame Safeguard - Perform a flame failure check and
“pilot” turndown test. See control manufacturer's bulletin
for further information.
4. Motor - Motor life will be increased by proper oiling.
There are provisions in both end shields for relubrication.
Re-oil each bearing with 150 drops (approximately 1 teaspoon) SAE-20 oil.
5. If the burner is to be out of service for the summer, turn
off the burner control switch and close the manual gas
cocks.
Flame Safeguard
See manufacturer's bulletin for more detailed information or
for information on flame safeguard other than the RM7897A.
The Honeywell RM17897A is a microprocessor based integrated burner control that will do self-diagnostics, troubleshooting, and status indication, as well as the burner
sequencing and flame supervision.
Keyboard Display Module
The Honeywell S7800A1001 module is an optional device
available for use with the RM7897A. It can be a permanent
accessory added to the RM7897A or it can be carried by the
service technician as a tool that is very easy to mount when
servicing the RM7897A. It mounts directly onto the
RM7897A and has a 2 row by 20 column display. The module will indicate flame signal dc volts, sequence status,
sequence time, hold status, lockout/alarm status, total hours
of operation, total cycles of operation, and can provide 127
different diagnostic messages for troubleshooting the system.
The module will give a fault history. It can be mounted to the
RM7897A and will retrieve information on the six most
recent faults.
Consult the Honeywell bulletin 65-0090-1 “7800 Series,
Keyboard Display Module” and 65-0118-1 “7800 Series,
System Annunciation, Diagnostics and Troubleshooting.”
IM 685-2
Operation
Initiate Period: When the relay module is powered it goes
through a 10 second “Initiate” period. It will also enter into
the “Initiate” period if electrical power problems such as low
voltage or momentary interruption occur while the unit is
operating. Operation of the burner fan motor is delayed
throughout the “Initiate” period.
Standby: After the initiate period is completed, the module
will enter the standby mode and await a call for heat by the
temperature control system.
occurs, the module will recycle within 3 seconds, and initiate
a new prepurge period. If pilot flame continues to be detected,
the module will be in Run until the power is interrupted to terminal 6, indicating that the temperature control system no
longer requires heat, or that the high limit or another control
has opened.
LED Display
There are five labeled LED's located on the front of the
RM7897A which are energized to indicate operation as follows:
Normal Start-Up
Prepurge: Upon a call for heat the prepurge period will
begin. If the air switch does not detect fan operation within 10
seconds into the prepurge, a recycle to the beginning of the
prepurge will occur.
POWER The RM7897A is powered.
Ignition Trial: The pilot gas valve and the ignition transformer are powered for 10 seconds following the prepurge.
Pilot flame must be proven at the end of that 10 second period
or a shutdown will occur.
MAIN The ignition trial period is complete, flame is
detected, and the terminal for the main gas valve is powered.
PILOT The prepurge period is complete and the terminal for
the pilot gas valve is powered.
FLAME Pilot flame is detected.
ALARM The RM7897A is on equipment protection lockout.
Run: If Pilot flame is proven at the end of the 10 second ignition trial. the main gas valve will be powered. If a flameout
IM 685-2
21
Troubleshooting Chart
The RM7897A flame safeguard is equipped with an LED to
aid in the diagnosis of burner operation and problems. Fault
identification is a series of fast- and slow-blinking LED lights.
The fast blinks identify the tens portion of the fault code (two
fast blinks is 20), while the slow blinks identify the units portion of the fault code (two slow blinks is 2). Two fast blinks
followed by two slow blinks would be fault code 22. This
identifies a flame signal absent at the end of the pilot flame
establishing period. (See Table 6 for Blinking Fault Code
List.) The LED code repeats as long as the fault exists. To
clear the fault, press the RESET button.
In addition, a Keyboard Display Module is available and is a
valuable aid for indicating flame signal DC volts, fault messages, sequence status, etc. See “Flame Safeguard” on page 20
for additional information on the Keyboard Display Module.
Some of the steps listed in this troubleshooting chart will be
unnecessary if a Keyboard Display Module is used, as that
module will pinpoint many problems.
Voltage checks can be accomplished without removing the
Flame Safeguard by removing the Electrical Access Slot
Covers on the side of the sub-base and then using those electrical access slots.
Table 5. Troubleshooting chart
BURNER MOTOR DOES NOT RUN (AFTER 10 SECOND “INITIATE” PERIOD AND WITH SWITCH AT AUTO):
1.1 Power LED is off.
Power is not getting to burner.
1.2 Entire unit seems to be off.
Burner power comes from the main control panel which has a main disconnect switch, a stepdown transformer with primary
winding fuses, a 120V secondary winding fuse, and an on-off service switch. If any of these were open, the burner as well as the
supply fan would be inoperative. The control system also has firestat type temperature sensors which will shut down the entire
unit if supply or return air temperatures exceed set points. On some control systems, the firestats only lock out the supply and
return fans. Check main control schematic, as these would not be burner problems.
1.3 Supply fan will operate.
1.4 Power LED is on.
a. Check the manual reset limit control located between the filters and the supply fan and reset if required.
b. Check that the control system has energized relay R20 located in the main control panel.
Push the reset button on the flame safeguard.
a. Check Table 6. The LED code may diagnose the problem.
b. Push the reset button on the burner motor.
(Note: If motor is hot and probably tripped, it has to cool sufficiently before it can be reset.)
1.5 Resetting flame safeguard
does not start motor after the 10
second “Initiate” period is completed.
c. Remove the left side electrical access cover on the flame safeguard sub-base and test for line voltage at terminal 4 and L2. If
powered, the problem is with the burner motor or its associated controls. On Models 1100-2000, terminal 4 only controls a
contactor and burner motor power comes from its own circuit breaker. If terminal 4 is dead, check for power to terminals 6 and
L2.
d. IF VOLTAGE IS ZERO: The power is being interrupted by the limit control, the manual reset high or auto reset low gas pressure switches (if included), the low fire end switch on the modulating operator (if included), or relay contact in the main control
system. Consult the schematic and determine the interruption.
e. If voltage is satisfactory at terminals 6 and L2 and terminal 4 does not become energized after 10 seconds, and pressing the
safety reset button has no effect, replace the RM7897A.
BURNER MOTOR RUNS, BUT...
2.1 Burner motor runs valve actuator travels to the maximum
rate position and stays there,
the Keyboard Display Module
indicates "Purge Hold".
a. Switch LS2 is not being actuated by the collar on the control rod when at the maximum rate position.
2.2 Burner motor runs, valve actuator travels to the maximum
rate position and stays there,
the Keyboard Display Module
goes through the prepurge
countdown. At approximately
20 seconds, Relay (R21) does
not energize.
a. Timer TD10 is not 'making' after 20 seconds. Check that there is 120 volts on TD10 tab 1 when the actuator is at the maximum rate position. TD10 tab 2 should become energized 20 seconds after tab 1 is powered.
2.3 Burner motor runs, prepurge
appears normal, LED marked
PILOT comes on for 10 seconds, then the flame safeguard locks out on flame
failure.
b. The air proving switch AS is not sensing burner fan pressure. Check the connecting tube, setpoint, and wiring. If LS2 and AS
are functioning, 120 volts can be measured across terminals 7 and L2 on the flame safeguard when the burner fan is running.
b. Relay R21 is not being energized by TD10, check for power across C1 and C2 after TD10 has become energized and replace
R21 if indicated.
a. Check Table 6. The LED code may diagnose the problem.
b. Flame is not igniting or is not being detected by the flame safeguard. Check that the manual gas valves are open. Check for
manifold pressure at Tap (1), Figure 16, during the 10 seconds the LED marked Pilot is on:
1. If zero, verify that there is pressure at Tap (2), Figure 16, during the same 10 second period. If so, check that LS1 is being
actuated by the collar on the control rod when at the low fire position. Check that the manual knob on GV1 is not closed
and power is supplied to valve.
2. If manifold pressure is normal, check for disconnected or shorted flame rod or ignition lead wire. Watch the ignition attempt
through inspection window on burner and check that spark is in the appropriate location. If not, this indicates a short. If
flame is observed but not detected by the flame safeguard, remove the burner gun assembly and check the flame rod,
lead wire, and connections.
3. Check the flame safeguard with a flame simulator:
a. Close main gas test cock.
b. Plug the flame simulator into the flame safeguard.
c. When the LED marked PILOT comes on, touch the simulator G post to ground. If the LED marked FLAME now comes
on, the flame safeguard is working, but it is not receiving an adequate flame signal. If the LED marked FLAME did not
come on, replace the R7847A amplifier and/or the RM7897A flame safeguard.
4. If there is spark but no flame, check for faults that would cause way too much air or too little gas.
22
IM 685-2
MOTOR RUNS, PILOT IGNITES...
a. Check Table 6. The LED code may diagnose the problem.
3.1 Burner motor starts. After 30
(60 or 90) seconds the PILOT
LED comes on, the FLAME
LED comes on momentarily
and then goes out.
b. The power is only momentarily proving itself to the flame safeguard. It must be proven at the end of the of the 10 second ignition trial.
c. On a new start-up, this could indicate the gas lines have not been sufficiently purged of air.
d. Improper flame rod position.
e. Improper pilot air or gas adjustments.
f. Air leakage into the pilot burner at the porcelain bushing or through cracks in pilot burner.
g. Defective or improperly installed pressure regulator upstream of pilot gas cock that passes enough gas for pilot, but when
main valve opens, gas pressure drops drastically.
a. Check that the main manual gas cocks are open.
3.2 Pilot operates, the flame
safeguard does not lock out.
but the main flame does not
come on.
b. If the Main LED does not come on, check the voltage at terminals 9 to L2. If no voltage across 9 to L2, replace the RM7897A.
c. Check for defective or improperly installed pressure regulators and determine that their vents are not plugged.
d. Check for defective or improperly installed main gas valves, or open wires to the valve.
e. On diaphragm type gas valves, check for plugged or misadjusted bleed orifice or bleed line.
BURNER OPERATES; HOWEVER...
4.1 Combustion tests indicate
CO2 and/or CO are not within
the expected range.
a. Measure gas manifold pressure at Port (1), Figure 16a, both at the maximum and minimum firing rate and correct if required.
See Table 7, Column (9) and (10).
b. Measure the burner air pressures at Port (4) and (5), Figure 16a and 16b. If readings are significantly different, from Table 7,
Columns (6), (7), and (8) determine why. Possible reasons include a clogged blower wheel, air leaks, or loosened components that could cause variations.
c. Combustion test should be performed when the furnace is at operating temperature (typically after 10 to 15 min.)
d. Models 040 and larger have multiple valves in parallel. Determine that they are all functioning. While operating at maximum
rate use the manual operator to momentarily close the valves one at a time while observing the manifold pressure. If a reduction in manifold pressure does not occur the valve was not open before the test.
4.2 At maximum firing rate, the
burner runs rough.
a. Gas manifold pressure is too high and furnace is being fired above its rated capacity. See “Verify Input Rate” on page 17. Also
check CO2 and CO levels.
b. The heat exchanger needs cleaning. Increased pressure drop through heat exchanger reduces airflow and affects
combustion.
c. Inspect gun assembly and blast tube for warpage or deterioration.
4.3 Flame is not symmetrical as
observed through rear
inspection window.
4.4 Nuisance tripping of the flame
safeguard.
a. Too high airflow relative to gas flow. Check gas manifold pressure. Check CO2 level.
b. Gun disc is not perpendicular to the blast tube, or gun disc is warped or otherwise out of alignment.
a. Check Table 6. The LED code may diagnose the problem.
b. Check gas pressure situation. Marginal pressure during normal times can become low pressure during time of peak demand
and lead to trip-outs, etc. Pressures higher than that for which the gas train is designed can also cause problems. Line pressure should not exceed 13.9' W.C. (½ psi) into the combination gas controls. Pressures higher than this require an additional
stepdown regulator to maintain the pressure below 13.9" W.C. even at "no flow" conditions. The preferred pressure to the
combination gas controls is 7.0 in. W.C. A regulator that does not shut off tight at "no flow" will allow a small amount of gas to
leak past and eventually the high pressure will build up on the downstream side, thus exceeding the rating of the gas train
components.
c. Undersized piping can also cause problems by delivering reduced pressure during times of maximum demand.
d. Check the flame signal while modulating from minimum to maximum firing rate.
e. Check the ignition electrode gap and orientation. Check the porcelain for cracks or other defects.
f. Observe the flame signal DC volts when turning on the burner switch. Any indications before the ignition cycle could indicate a
short to ground. This could be an intermittent situation from moisture conditions. With line gas cock closed any movement
during the ignition attempt would indicate ignition interference.
g. Check supply voltage and if suspicion warrants arrange to have a recording voltmeter connected to the burner for a period
of time.
h. Marginal flame signal. Adjust flame rod position.
i. Check the ground path from FSG terminal G to the burner gun assembly. A wire runs from G to the ground screw on the left
side of the burner air box. The path continues through the variable orifice valve through the union to the burner gun assembly.
4.5 Main flame comes on at low
fire, but as actuator attempts
to reposition for an increased
firing rate the flame goes out.
Then the sequence is
repeated.
a. Check Table 6. The LED code may diagnose the problem.
4.6 At the instant spark comes
on, the flame safeguard
drops out and restarts the
pre-purge cycle.
Ignition interference. Flame rod or its wire is sensing voltage from ignition. Also verify that ignition electrode spark gap is within
specifications.
4.7 When the flame safeguard is
powered it locks out and the
ALARM LED comes on.
a. Purge card missing or bad, terminals are energized that should not be at that stage, or there is an internal system fault.
Replace purge card or RM7897A as indicated.
IM 685-2
b. Check the burner fan air proving switch and tube. As the burner air control valve opens further to provide more air for an
increased firing rate, the static pressure inside the air valve box is reduced. This is the pressure being sensed by the air proving switch, and if it falls below its set point the burner will drop out. The adjustment screw is located next to the wiring box
cover. Turn screw CCW to reduce set point.
c. Use a manometer to determine if the gas pressure at the orifice is dropping prior to the flame going out. If gas pressure is
dropping, check for a plugged vent on a gas pressure regulator or something that restricts the gas flow in the line so only a
low firing rate can occur. Also see 4.1d.
23
Table 6. Fault codes
BLINKING FAULT CODES...
Fault Code
System Failure
Code 1-1
*Low AC Line
Low AC Line detected.
Voltage*
Code 1-2
*AC Quality
Problem*
Excessive noise or
device running on slow,
fast, or AC line dropout
a. Check the relay module and display module connections.
b. Reset and sequence the Relay Module.
c. Check the 7800 power supply and make sure that frequency and voltage meet specifications.
d. Check the backup power supply, as appropriate.
detected.
a. Check that flame is not present in the combustion chamber; correct any errors.
b. Make sure that the flame amplifier and flame detector are compatible.
Code 2-1
Flame sensed when no
c. Check the wiring and correct any errors.
*Unexpected
flame is expected during
d. Remove the flame amplifier and inspect its connections. Reseat the amplifier.
Flame Signal*
STANDBY or PURGE.
e. Reset and sequence the relay module.
f. If the code reappears, replace the flame amplifier and/or the flame detector.
g. If the fault persists, replace the relay module.
a. Measure the flame signal. If one exists, verify that it meets specifications.
b. Make sure that the flame amplifier and flame detector are compatible.
Code 2-2
*Flame Signal
Absent*
No-flame time present
c. Inspect the main fuel valve(s) and valve connection(s).
at the end of the PIlot
d. Verify that the fuel pressure is sufficient to supply fuel to the combustion
Flame Establishing
chamber. Inspect the connections to the fuel pressure switches. Make sure they are functioning properly.
Period; lost during the
e. Inspect the Airflow Switch and make sure that it is functioning properly.
Main Flame Establishing
f. Check the flame detector sighting position; reset and recycle. Measure the flame signal strength. Verify
that it meets specifications. If not, refer to the flame detector and/or flame amplifier checkout procedures
in the installation instructions.
Period or during RUN.
g. Replace the flame amplifier and/or the flame detector, if necessary.
h. If the fault persists, replace the relay module.
a. Make sure the flame detector and flame amplifier are compatible.
b. Remove the flame amplifier and inspect its connections. Reset the flame amplifier.
Code 2-3
*Flame Signal
Overrange*
c. Reset and sequence the relay module.
Flame signal value is
too high to be valid.
d. Check the flame detector sighting position; reset and recycle. Measure flame strength. Verify that it meets
specifications. If not, refer to the flame detector and/or flame amplifier checkout procedures in the installation instructions.
e. If the code reappears, replace the flame amplifier and/or the flame detector.
f. If the fault persists, replace the relay module.
a. Check wiring; correct any errors.
Code 3-1
*Running/
Interlock Switch
Problem*
b. Inspect the fan; make sure there is no air intake blockage and that it is supplying air.
Running or Lockout
Interlock fault during
Prepurge.
c. Make sure the Lockout Interlock switches are functioning properly and the contacts are free from contaminants.
d. Reset and sequence the relay module to Prepurge (place the TEST/RUN Switch in the TEST position, if
available). Measure the voltage between terminal 7 and G (ground); 120 Vac should be present. Switch
TEST/RUN back to RUN.
e. If steps 1 through 4 are correct and the fault persists, replace the relay module.
a. Check wiring to make sure that the Lockout Interlocks are connected properly between terminals 6 and 7.
Correct any errors.
Code 3-2
*Running/
Interlock On
During
Standby*
Lockout Interlock
b. Reset and sequence the relay module.
powered at improper
c. If the fault persists, measure the voltage between terminal 6 and G (ground), then between terminal 7 and
G. If there is 120 Vac at terminal 6 when the controller is off, the controller switch may be bad or is jumpered.
point in sequence or On
in Standby.
d. If steps 1 through 3 are correct and there is 120 Vac at terminal 7 when the controller is closed and the
fault persists, check for a welded or jumpered Running Interlock or Airflow Switch. Correct any errors.
e. If steps 1 through 4 are correct and the fault persists, replace the relay module.
a. Check wiring, making sure upstream valve is connected to terminal 9 and downstream valve is connected
to terminal 17.
Code 3-3
VPS (Valve Proving
b. Conduct Valve Seat leakage test using a manometer.
*VPS in
Switch) in wrong state
Improper State*
during VPS Test.
c. Reset and sequence the relay module; if fault repeats, test VPS (connected to terminal 16) is functioning
properly; replace if necessary.
d. Reset and sequence the relay module.
e. If fault persists, replace the relay module.
24
IM 685-2
a. Make sure the purge card is seated properly.
Code 4-1
*Purge Card
Problem*
No purge card or the
b. Inspect the purge card and the connector on the relay module for any damage or contaminants.
purge card timing has
c. Reset and sequence the relay module.
changed from the
d. If the fault code reappears, replace the purge card.
original configuration.
e. Reset and sequence the relay module.
f. If the fault code persists, replace the relay module.
WARNING
Electrical Shock Hazard; Fire or Explosion Hazard.
Code 4-2
*Wiring
Problem/
Internal Fault*
Pilot (ignition) valve
Can cause severe injury, death or property damage.
terminal, main valve,
Remove system power and turn off power supply.
ignition or Main Valve 2
was on when it should
a. Remove system power and turn off fuel supply.
be off.
b. Check wiring; correct any errors.
c. inspect Pilot Fuel Valve(s), both places, and connections.
d. Reset and sequence the relay module.
e. If the fault persists, replace the relay module.
a. Check wiring; correct any errors.
Code 4-3
*Flame
Amplifier
Problem*
Flame not sensed,
sensed when it should
be on or off.
b. Make sure the flame amplifier and flame detector are compatible.
c. Remove the flame amplifier and inspect the connections. Reseat the amplifier.
d. Reset and sequence the relay module.
e. If the code reappears, replace the flame amplifier and/or the flame detector.
f. If the fault persists, replace the relay module.
Code 4-4
*Configuration
Jumper
Problem*
The configuration
a. Inspect the jumper connections. Make sure the clipped jumpers were completely removed.
jumpers differ from the
b. Reset and sequence the relay module.
sample taken at startup.
c. If the fault persists, replace the relay module.
a. Check wiring and correct any errors.
Code 5-1
*Preignition
Interlock*
Preignition Interlock
fault.
b. Check Preignition Interlock switches to assure proper functioning.
c. Check fuel valve operation.
d. Reset and sequence the relay module; monitor the Preignition Interlock status.
e. If the fault persists, replace the relay module.
a. Check wiring and correct any errors.
Code 5-2
*High Fire Sw.
or Low Fire
Sw.*
Either High Fire Switch
or Low Fire Switch
failure.
b. Reset and sequence the relay module.
c. Use manual motor potentiometer to drive the motor open and closed. Verify at motor switch that the end
switches are operating properly. Use RUN/TEST switch if manual potentiometer is not available.
d. Reset and sequence the relay module.
e. If the fault persists, replace the relay module.
a. Check wiring and correct any errors.
Code 5-3
Man-Open Switch, Start
b. Make sure that the Manual Open Valve Switch, Start Switch and Control are operating properly.
*Man-Open
Switch or Control On in
c. Stat Switch held On too long.
Sw.; Start Sw.
the wrong operational
d. Reset and sequence the relay module.
or Control On*
state.
e. Reset and sequence the relay module. If the fault persists, replace the relay module (RM7838A1014;
RM7838B1013 or RM7838C1004 only).
Code 6-1
Relay Module self-test
*Internal Faults*
failure.
a. Reset and sequence the relay module.
b. If fault reappears, remove power from the device, reapply power, then reset and sequence the relay module.
c. If the fault persists, replace the relay module.
a. Reset and sequence the relay module.
Code 6-2
Relay Module Self-Test
*Internal Faults*
failure.
b. If fault reappears, remove power from the device, reapply power, then reset and sequence the relay module.
c. If fault does not repeat on the next cycle, check for electrical noise being copied into the relay module
through the external loads or possibly an electrical grounding issue.
d. If the fault persists, replace the relay module.
IM 685-2
25
Typical Parts List - 60 Hz
QTY.
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
3
1
1
1
2
1
1
1
1
1
1—6
1
1
1
1
26
MCQUAY
PART NO.
0342492-00
0322486-00
0322484-00
0348611-02
0348611-01
0342480-04
0330038-00
0344826-00
0733371-01
0733371-02
0733008-03
0733009-01
073301O-03
0733007-02
0598677-01
0347430-02
0347430-03
0598678-01
0347429-02
0365185-02
0964148-01
0964148-02
0964148-03
0964148-04
0964148-05
0964148-06
0964148-08
0964148-10
0964148-1 1
0964148-12
0964148-13
0964148-14
0373788-02
0341017-03
0341017-07
0341017-06
0351647-01
0341020-00
0341019-00
0196430-00
0274007-00
0274007-00
0282101-06
0599753-01
0335367-00
0004981-00
0599887-00
0599888-00
0479361-10
0733365-04
0598613-01
0594700-01
0598621-10
0964149-01
Emerson
Emerson
Emerson
Beckett
VENDOR
PART NO.
4526
457
458
22031-07
Antones
Allison
W/R
W/R
HW
HW
HW
HW
SMP 4130
1092
5A75-1 0
5A75-12
RM7897A1014
R7847A1033
ST7800A1054
Q7800A1005
RBM
RBM
RBM
SSAC
OMRON
McGill
91 -131006-13000
184-20202-101J
184-20202-101J
TAC1420
V-10G5-1C24-K
0140-4000
HW
HW
M6161A1004
VR4305M4540
VENDOR
USED ON
MODELS HT ***
020 — 080
100 — 150
200
020 — 080
100 — 150
200
020 — 200
020 — 200
032 — 200
020 — 025
020 — 200
020 — 200
020 — 200
020 — 200
020 — 200
020 — 100
110 — 200
020 — 200
020 — 100
110 — 200
020
025
032
040
050
064 — 065
079 — 080
100
110
140
150
200
020 — 040
050
064 — 100
110 — 140
150 — 200
020 — 100
110 — 200
020 — 200
020 — 200
110 — 200
020 — 200
020 — 200
020 — 200
020 — 200
050 — 100
110 — 200
020 — 200
020 — 200
020 — 200
020 — 200
020 — 200
020 — 200
DESCRIPTION
Burner Fan:
Burner Fan Wheel:
Motor 1/4 hp, 3450 rpm
Motor 1/2 hp, 3450 rpm
Motor 3/4 hp, 3450 rpm
6.25 x 3.438 (.500”)
7.09 x 3.160(.625")
7.50 x 3.160 (.625")
Air Switch
Ignition Transformer
Fan Limit Control
Fan Limit Control
Flame Safeguard (less amplifier & timer)
Amplifier Only (3 seconds)
Timer Only (60 seconds)
Subbase for Flame Safeguard
Flame Rod Assembly
Flame Rod Lead Wire Assembly
Flame Rod Lead Wire Assembly
Ignition Electrode Assembly
Ignition Electrode Cable
Ignition Electrode Cable
Burner Gun Assembly
Burner Gun Assembly
Burner Gun Assembly
Burner Gun Assembly
Burner Gun Assembly
Burner Gun Assembly
Burner Gun Assembly
Burner Gun Assembly
Burner Gun Assembly
Burner Gun Assembly
Burner Gun Assembly
Burner Gun Assembly
Blast Tube Assembly, 4.00 x 20°
Blast Tube Assembly, 5.00 x 20°
Blast Tube Assembly, 5.00 x 27½°
Blast Tube Assembly, 7.00 x 27½° (Sm)
Blast Tube Assembly, 7.00 x 27½° (Lg)
Blast Tube Gasket, 4-5"
Blast Tube Gasket, 7"
Relay R20, R21, R23, DPDT 120 volt
Relay R22, SPST/NO 120 volt
Contactor M29
Timer TD10
Switch LS1 & LS2
Switch S3, Toggle 4PST
Grommet 0.380 ID, Base Air Tube
Grommet 0.750 ID, Pri Air Tube
Grommet 1.125 ID, Pri Air Tube
Actuator, Floating
Combination Gas Control
Control Rod, Sliding Bushing
Shoulder Screw
Crank Arm Extension
Air Damper Flex Link
IM 685-2
IM 685-2
(2)
(3)
250
312
400
500
625
800
812
1000
1000
1250
1375
1750
1875
2500
@ Max.
Rate
12.5
15.6
20.0
25.0
31.3
40.0
40.6
50.0
50.0
62.5
68.8
87.5
93.8
125.0
Note 4
@ Min.
Rate
Note 3
Input MBH or CFH
2,300
3,800
2,950
6,000
4,600
9,600
5,970
12,000
7,340
15,000
10,100
21,000
13,700
30,000
(5)
80
61
100
61
100
61
100
61
100
61
100
61
100
61
Max.
TR
Deg F
Furnace
Min.
CFM
(4)
Key:
(1) Gas Manifold Pressure Tap (1/8 inch l.P.)
(2) Gas Line Pressure Tap (1/8 inch l.P.)
(3) Gas Pressure Regulator Adjustment
(4) Burner Box Air Pressure Port
(5) Air Valve Pressure Port (On Box Bottom)
(6) Firing Rate Indicator Scale
(7) Optional Additional Gas Valve(s)
(8) Optional High Pressure Regulator
(9) Optional Low Gas Pressure Switch
(10) Optional High Gas Pressure Switch
(11) Combination Gas Control
(12) Shoulder Screw Attaching Bushing To Crankarm
Notes:
1. Pressure to obtain 100% input with standard UL
gas train. For IRI, add 1.00 in. W.C.
2. Gas inlet pressures over 0.50 PSI (13.9 in. W.C.,8
oz./sq. in.) require an additional high pressure
regulator.
3. CFH of natural gas @ 1000 BTU/cu. ft.
4. At minimum firing rate the MBH should be 90 to
100% of this value.
5. This is approximate. A higher reading indicates
multiple valves are not in balance. See section on
“Gas Valve Pressure Regulator Adjustment.”
HT 020
HT 025
HT 032
HT 040
HT 050
HT 064
HT 065
HT 079
HT 080
HT 100
HT 110
HT 140
HT 150
HT 200
Burner
Model
No.
(1)
Table 7. Capacities and dimensions
FSG
5
8
Figure16a.
1.48
1.95
2.34
2.74
2.49
2.15
1.55
1.64
1.40
2.09
2.60
2.45
2.50
3.65
@ Max. Rate
@ Max. Rate
1.59
1.95
2.30
2.69
2.43
2.04
1.62
1.62
1.45
1.63
2.50
2.25
2.32
2.60
Burner
Operating
During
Prepurge
SUPER
(7)
Air Pressure (In. W.C.)
In Box
Measured: At Port 4
(6)
MOD
6
9
3.80
3.71
3.50
3.29
3.42
3.50
3.44
3.66
3.48
4.60
4.45
4.45
4.50
4.90
@ Max. Rate
During
Prepurge
At Port 5
In Valve
(8)
1
12
7
3
2
3.01
3.46
2.94
4.14
2.98
2.86
2.89
3.45
3.14
3.20
2.90
2.80
3.10
3.70
11
10
3.12
3.55
3.21
4.39
3.25
3.22
3.33
3.84
3.45
3.72
3.50
3.30
3.60
4.10
Note 5
4.5
5.5
6.0
5.0
5.5
7.0
7.0
6.5
6.5
6.5
5.0
5.0
5.0
6.0
Note 1, 2
0.75
0.75
0.75
1.00
1.00
1.25
1.25
1.25
1.25
1.25
1.50
1.50
1.50
2.00
To 0.5
0.75
0.75
0.75
1.00
1.00
1.25
1.25
1.25
1.25
1.25
1.25
1.25
1.25
1.50
Note 2
2—3
4
0.75
0.75
0.75
1.00
1.00
1.25
1.25
1.25
1.25
1.25
1.25
1.25
1.25
1.25
Note 2
5 — 10
Inlet Pressure (PSI)
(13)
(14)
(15)
Gas Connection Size (IP)
Figure 16b.
3.4
3.5
3.5
3.6
3.6
3.8
3.8
4.0
4.0
7.5
7.8
7.8
8.4
11.2
(9)
(10)
(11)
(12)
Gas Pressure (in. W.C.)
Burner
Manifold
Supply Running
Measure at Tap (1)
Line
Current
@ Min. Measure @
@ Max.
Rate
Tap (2)
Rate
Amps
Capacities and Adjustments
27
28
Reference Number:
(1) Initial Startup of Furnace
27
28
(1)
* Tap Locations are shown as (2) and (9) on Figure 16.
(Summarize
any service
work
performed)
Comments
Flue Gas CO (PPM)
Air Pressure in Box (In. W.C.)
Gas Manifold Pressure (In. W.C.)*
Gas Line Pressure (In. W.C.)*
Flame Signal (DC Volts)
Ambient Temperature (Deg. F)
Flue Gas Temperature (Deg. F)
Flue Gas CO2 (percent)
Flue Gas CO (PPM)
Air Pressure in Box (In. W.C.)
Gas Manifold Pressure (In. W.C.)*
Gas Line Pressure (In. W.C.)*
Flame Signal (DC Volts)
Ambient Temperature (Deg. F)
Flue Gas Temperature (Deg. F)
Flue Gas CO2 (percent)
Burner Motor Amps
Flue Gas CO (PPM)
Air Pressure i Box (In. W.C.)
Burner Motor VoIts
Gas Manifold Pressure (In. W.C.)*
Gas Line Pressure (In. W.C.)*
Flame Signal (DC Volts)
Ambient Temperature (Deg. F)
Flue Gas Temperature (Deg. F)
Flue Gas CO2 (percent)
Description of
Reading
19
20
21
22 Min. Rate
23 Scale = 5
24
25
26
11
12
13
14 Mid. Rate
15 Scale = 50
16
17
18
1
2
3
4
5 Max. Rate
6 Scale = 100
7
8
9
10
Firing
Rate
Date of Readings
Performance & Service History
Table 8. Service history
IM 685-2
McQuay Training and Development
Now that you have made an investment in modern, efficient McQuay equipment, its care should be a high priority.
For training information on all McQuay HVAC products, please visit us at www.mcquay.com and click on training, or
call 540-248-9646 and ask for the Training Department.
Warranty
All McQuay equipment is sold pursuant to its standard terms and conditions of sale, including Limited Product
Warranty. Consult your local McQuay Representative for warranty details. Refer to Form 933-43285Y. To find your
local McQuay Representative, go to www.mcquay.com.
This document contains the most current product information as of this printing. For the most up-to-date product
information, please go to www.mcquay.com.
© 2007 McQuay International • www.mcquay.com • 800-432-1342