surelight® ignition system important caution

Service Literature
Corp. 0222−L7
Revised 11−2006
SURELIGHT®
IGNITION SYSTEM
TWO STAGE IGNITION SYSTEM
& TWO STAGE VARIABLE SPEED IGNITION SYSTEM
I−GENERAL
The two stage SureLight (figure 1 )and two stage variable
speed SureLight (figure 2 ) ignition systems, consists of a
Lennox control board and hot surface ignitor. Both type
control boards are similar except the two stage variable
speed board controls an ICM2 indoor blower motor.
Boards and ignitor work in combination to ensure furnace
ignition and ignitor durability. Boards control all major furnace operations. Tables 1 through 4 show jack plug
terminal designations.
Two stage boards 18M3401 and 46M9901 featuretwo
LED lights, DS1 and DS2 for troubleshooting (see table 5
for diagnostic codes). The boards also have two accessory terminals rated at (1) one amp each. Terminal EAC
energizes an electronic air cleaner with the indoor blower.
Terminal HUM energizes the humidifier when CAI is energized on a call for heat. The SureLight board has a built in
heating isolation relay. See wiring diagram for heat anticipator settings.
Two stage board 100869 features a red LED light, for furnace status and troubleshooting. The LED flashes in X" +
Y" codes. For example using table 7 under PRESSURE
SWITCH CODES", if the red LED flashes 2 times, then off
for 2 seconds then flashes 3 times, the low pressure
switch is failed open. The board also has two 120 volt accessory terminals rated at (1) one amp each. In addition
there is a 24 volt humidifier terminal located on TB1.
Two stage variable speed boards 18M9901 and
49M5901 features two LED lights, DS1 and DS2 for troubleshooting (see table 5 for diagnostic codes) and four
LED lights (DS3, DS6, DS7 and DS8) to show furnace status (see table 6 for status codes). The boards also have
two accessory terminals rated at (1) one amp each. Terminal EAC energizes an electronic air cleaner with the
indoor blower. Terminal HUM energizes the humidifier
when CAI is energized on a call for heat. The SureLight
board has a built in heating isolation relay. See wiring diagram for heat anticipator settings.
Page 1
Two stage variable speed board 100870 features a red
LED light, for furnace status and troubleshooting. The
LED flashes in X" + Y" codes. For example using table 7
under PRESSURE SWITCH CODES", if the red LED
flashes 2 times, then off for 2 seconds then flashes 3
times, the low pressure switch is failed open. Two green
LEDs show indoor blower status and CFM. See for more
detail. The board also has two 120 volt accessory terminals rated at (1) one amp each. In addition there is a 24 volt
humidifier terminal located on TB1.
IMPORTANT
Ignition control will not operate unless unit is
properly grounded. 120V supply must be
installed with correct polarity.
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
CAUTION
Electrostatic discharge can affect electronic
components. Take precautions during furnace
installation and service to protect the furnace’s
electronic controls. Precautions will help to
avoid control exposure to electrostatic discharge by putting the furnace, the control and
the technician at the same electrostatic potential. Neutralize electrostatic charge by touching
hand and all tools on an unpainted unit surface,
such as the gas valve or blower deck, before performing any service procedure.
Table of Contents
I General Information . . . . . . . . . . . . . .
Board Terminal Designations . . . . . . . .
Board Diagnostic Codes . . . . . . . . . . . .
II Operation . . . . . . . . . . . . . . . . . . . . . . .
III Additional Components . . . . . . . . . .
IV Diagrams . . . . . . . . . . . . . . . . . . . . . .
V Troubleshooting Flowcharts . . . . . . .
Page 1
Page 4
Page 5
Page 7
Page 13
Page 14
Page 22
© 2002 Lennox Industries Inc.
TWO−STAGE INTEGRATED CONTROL BOARD
18M3401 & 46M9901
1/4" QUICK CONNECT TERMINALS
NEUTRAL
LINE − 120 VAC
XFMR − Transformewr
EAC − Electronic Air Cleaner
CIRC − Indoor Blower
HUM − Humidifier
HOT
HUM − Humidifier
XFMR − Transformer
LINE − 120 VAC
PARK − Unused Leads
COOL − Cooling Speed
EAC − Electronic Air Cleaner
HI HEAT − High Heat Speed
LO HEAT − Low Heat, Low Cool, Cont. Blower Speed
LEDs
DIP
SWITCHES
1−4
E20
JUMPER
FLAMESENSE
(120V)
THERMOSTAT CONNECTIONS (TB1)
JUMPER W915
DIP SWITCH(ES)
FUNCTION
1 and 2
Blower Off Delay (Heating Mode)
3
Second Stage ON Delay (Single−stage t’stat)
4
Blower Off Delay (Cooling Mode)
TWO−STAGE INTEGRATED CONTROL BOARD
100869
FLAME
5
1/4" QUICK CONNECT TERMINALS
SENSE
(120V)
1
SENSE = 120 VAC OUTPUT TO FLAME SENSER
NEUTRALS= 120 VAC NEUTRAL
PARK = DEAD TERMINAL FOR UNUSED BLOWER LEAD
HEAT LOW = 120 VAC OUTPUT TO CIRC BLWR −− LOW HT SPEED
HEAT HIGH/ COOL LOW = 120 VAC OUTPUT TO CIRC BLWR −−
HIGH HEAT AND LOW COOL SPEED
COOL HIGH = 120 VAC OUTPUT TO CIRC BLWR −− HIGH COOL SPEED
DIAGNOSTIC
LEDs
THERMOSTAT CONNECTIONS (TB1)
1
5
DIP
SWITCHES
ON−BOARD
JUMPERS
FUTURE USE
1 4 7 10
1= ERROR CODE RECALL
H= 24V HUMIDIFIER OUTPUT DURING HEAT DEMAND
L= LENNOX SYSTEM OPERATION MONITOR
DIP SWITCH FUNCTIONS
W915
W951
DIP SWITCH(ES)
1 −− 2 Stage T’stat
2 −− 2nd Stage Delay
3 & 4 −− Heat Off Delay
5 −− Cool Off Delay
FIGURE 1
Page 2
FUNCTION
Selects t/stat type (single or two−stage)
Second stage ON delay (single−stage t’stat)
Heating fan OFF delay
Cooling fan OFF delay
TWO−STAGE VARIABLE SPEED INTEGRATED CONTROL BOARD
18M9901 & 49M5901
1/4" QUICK CONNECT TERMINALS
DIAGNOSTIC
LEDs
NEUTRAL
LINE − 120 VAC
XFMR − Transformewr
EAC − Electronic Air Cleaner
CIRC − Indoor Blower
HUM − Humidifier
HOT
HUM − Humidifier
XFMR − Transformer
LINE − 120 VAC
CIRC − Indoor Blower
EAC − Electronic Air Cleaner
DIP
SWITCHES1 − 3
E20
JUMPER
FLAME SENSOR
(120V)
THERMOSTAT CONNECTIONS (TB1)
DS8
DIP
SWITCHES
5 − 12
LEDs
ON BOARD
JUMPER
W915
DS7
DS3
LED
DS6
ON−BOARD
JUMPER W914
(cut when CCB1 or
Harmony II are used)
16 PIN BLOWER
CONTROL TERMINALS
DIP SWITCH FUNCTIONS
ON−BOARD
JUMPER W951
(cut when heat pump is
used with FM21)
DIP SWITCH(ES)
FUNCTION
1 and 2
Blower Off Delay
3
Second Stage ON Delay (Single−stage t’stat)
4
Not used
5 and 6
Cooling Mode Blower Speed
7 and 8
Blower Speed Adjustment
9 and 10
Cooling Mode Blower Ramping Profile
11 and 12
Heating Mode Blower Speed
TWO−STAGE VARIABLE SPEED INTEGRATED CONTROL BOARD
100870
1/4" QUICK CONNECT TERMINALS
FLAME
SENSE
(120V)
NEUTRALS= 120 VAC NEUTRAL
THERMOSTAT CONNECTIONS (TB1)
ON 1
9
12
DIAGNOSTIC
LEDs
5
16
8
ON
1 4
INDOOR
BLOWER DIP
SWITCHES
HEATING
DIP
SWITCHES
FUTURE USE
1
4 7 10
W915
W951
W914
H= 24V HUMIDIFIER OUTPUT DURING HEAT DEMAND
L= LENNOX SYSTEM OPERATION MONITOR
1= ERROR RECALL
ON−BOARD
JUMPERS
DIP SWITCH FUNCTIONS
HTG DIP SWITCH(ES)
1
2
3 and 4
INDOOR BLOWER
DIP SWITCH(ES)
5 and 6
7 and 8
9 and 10
11 and 12
FIGURE 2
Page 3
FUNCTION
T’stat Heat Stages (single or two−stage)
Second Stage ON Delay (single−stage t’stat)
Heating Fan OFF Delay
FUNCTION
Cooling Mode Blower Speed
Blower Speed Adjustment
Cooling Mode Blower Ramping Profile
Heating Mode Blower Speed
TABLE 1
SureLight 18M3401, 46M9901, 18M9901, 49M5901
TABLE 3
SureLight 100869, 100870
Two Stage & Two Stage Variable Speed Control
12Pin Terminal Designation
Two Stage & Two Stage Variable Speed Control
12Pin Terminal Designation
PIN #
Function
PIN #
Function
1
Gas Valve 2nd. Stage (High Fire)
1
Gas Valve 2nd. Stage (High Fire)
2
Second Stage Pressure Switch
2
Second Stage Pressure Switch
3
Not Used
3
Rollout In
4
Ground
4
Ground
5
24V Hot
5
24V Hot
6
Primary Limit In
6
Primary Limit In
7
Gas Valve 1st. Stage (Low Fire)
7
Gas Valve 1st. Stage (Low Fire)
8
Gas Valve Common
8
Gas Valve Common
9
24V Neutral
9
24V Neutral
10
Ground
10
Ground
11
Primary Limit Out
11
Rollout Out / Limit Out
12
1st Stage Pressure Switch
12
1st Stage Pressure Switch
TABLE 2
All SureLight Ignition Control Boards
TABLE 4
SureLight 18M9901, 49M5901, 100870
Two Stage & Two Stage Variable Speed Contol
5 Pin Terminal Designation
Two Stage Variable Speed Control Board
16 Pin Blower Control Terminals
PIN #
Function
1
Ignitor
2
Combustion Air Inducer High Speed
PIN #
Function
1
Ground
2
Low Heat Speed
3
Combustion Air Inducer Low Speed
4
Combustion Air Inducer Neutral
3
Ground
5
Ignitor Neutral
4
DELAY" Dip Switch Selection
5
COOL" Dip Switch Selection
Page 4
6
Y1" Signal
7
ADJUST" Dip Switch Selection
8
Ground
9
O" From Thermostat
10
DS" Output Signal
11
HEAT" Dip Switch Selection
12
24 VAC
13
HIGH HEAT Speed
14
Y2" Signal
15
G"
16
CFM LED
TABLE 5
SureLight® Boards 18M3401, 46M9901, 18M9901, 49M5901
DIAGNOSTIC CODES
Diagnostic LEDs are labeled DS1 and DS2. See figure 1
for location of diagnostic LEDs.
DS1
DS2
SIMULTANEOUS
SLOW FLASH
SIMULTANEOUS
SLOW FLASH
Power on − Normal operation.
Also signaled during cooling and continuous fan.
SIMULTANEOUS
FAST FLASH
SIMULTANEOUS
FAST FLASH
Normal operation − signaled when heating demand initiated at thermostat.
SLOW FLASH
ON
OFF
SLOW FLASH
Low pressure switch open;
OR: Blocked inlet/exhaust vent;
OR: Low pressure switch closed prior to activation of combustion air inducer.
OFF
FAST FLASH
High pressure switch open;
OR: Blocked inlet/exhaust vent;
OR: High pressure switch closed prior to activation of combustion air inducer.
ALTERNATING
SLOW FLASH
ALTERNATING
SLOW FLASH
Watchguard −− burners failed to ignite; OR limit open more than 3 minutes;
OR lost flame sense 5 times in one heating cycle;
OR pressure switch opened 5 times in one heating cycle.
SLOW FLASH
OFF
Flame sensed without gas valve energized.
ON
ON
OFF
ON
OFF
ON
Circuit board failure or control wired incorrectly. Check 24 and 115 volts to board.
FAST FLASH
SLOW FLASH
Main power polarity reversed. Switch line and neutral.
SLOW FLASH
FAST FLASH
Low flame signal. Measures below 0.2 microAmps. Replace flame sense rod.
ALTERNATING
FAST FLASH
The following conditions are sensed during the ignitor warm−up period only:
1) Improper main ground;
2) Broken ignitor; OR: Open ignitor circuit;
3) Line voltage below 75 volts.
(If voltage lower than 75 volts prior to ignitor warm-up, control will signal waiting on
call from thermostat, and will not respond.
ALTERNATING
FAST FLASH
DESCRIPTION
Primary, secondary or rollout limit switch open. Limits must close within 3 minutes
or unit goes into 1 hour Watchguard.
NOTE − Slow flash rate equals 1 Hz (one flash per second). Fast flash rate equals 3 Hz (three flashes per second).
Minimum flame sense current = 0.15−0.17 microAmps.
TABLE 6
SureLight Boards 18M9901, 49M5901
STATUS CODES
STATUS LED
COLOR
FUNCTION
DS3
ON / OFF ’
GREEN
DS3−ON indicates that the motor has a demand to operate. (This LED must be on in all
modes).
DS6
CFM"
GREEN
DS6−blinking indicates the airflow (CFM) demand in the motor. The air flow is determined by
counting blinks between two (2) second pauses. One blink equals roughly 100 CFM.
DS7
HI / LO"
YELLOW
DS7−ON indicates the DS to R" jumper has not been cut. When the jumper is cut the system
will be operating with LENNOX HARMONY IIt (See Harmony Installation Instructions) or
with a humidity control.
Humidity control: When ON, a 24 VAC is being applied and when OFF, it has been removed.
This on/off operation varies the indoor blower’s performance so dehumidification can be
enhanced.
DS8
HEAT"
YELLOW
DS8−ON indicates the system is in HEAT mode.
Page 5
TABLE 7
100869, 100870
SureLight® Boards
FLASH CODE
(X + Y)
STATUS / ERROR DESCRIPTION
FLASH CODE DESCRIPTIONS
Pulse
A 1/4 second flash followed by four seconds of off time.
Heartbeat
Constant 1/2 second bright and 1/2 second dim cycles.
X+Y
LED flashes X times at 2Hz, remains off for two seconds, flashes Y times at 2Hz, remains off for four
seconds, then repeats.
Pulse
Power on − Standby.
Heartbeat
Normal operation − signaled when heating demand initiated at thermostat.
FLAME CODES
1+2
Low flame current −− run mode.
1+3
Flame sensed out of sequence −− flame still present.
2+3
Low pressure switch failed open.
2+4
Low pressure switch failed closed.
2+5
High pressure switch failed open.
2+6
High pressure switch failed closed.
2+7
Low pressure switch opened during ignition trial or heating demand.
3+1
Limit switch open.
4+1
Watchguard −− Exceeded maximum number of retries.
4+2
Watchguard −− Exceeded maximum number of retries or last retry was due to pressure switch opening.
4+3
Watchguard −− Exceeded maximum number of retries or last retry was due to flame failure.
4+5
Watchguard −− Limit remained open longer than three minutes.
4+6
Watchguard −− Flame sensed out of sequence; flame signal gone.
4+7
Ignitor circuit fault −− Failed ignitor or triggering circuitry.
4+8
Low line voltage.
5+1
Hard lockout −− Rollout circuit open or previously opened.
5+2
Control failed self check, internal error (control will restart if error recovers).
5+3
No Earth ground (control will restart if error recovers).
5+4
Reversed line voltage polarity (control will restart if the error recovers).
5+6
Low secondary (24VAC) voltage.
PRESSURE SWITCH CODES
LIMIT CODE
WATCHGUARD CODES
HARD LOCKOUT CODES
Error Code Storage
The ignition control stores the last ten error codes in
memory. The codes are retained in case of power loss.
Error Code Review
1 − Short R (2) to (1). Within 1/2 second, the STATUS LED
will stay lit continuously to indicate that the short was
sensed.
2 − Continue to hold the short between R (2) to (1). After 5
seconds, STATUS LED will go from being continuously
lit to off. This indicates that error code review is pending.
3 − Remove R (2) to (1) short within ten seconds of STATUS LED turning off. This activates error code review.
5 − After final error code is indicated, STATUS LED will
flash to indicate normal operation.
Clearing Error Codes
1 − Short R (2) to (1). Within 1/2 second, the STATUS LED
will stay lit continuously to indicate that the short was
sensed.
2 − Continue to hold the short between R (2) to (1). After 5
seconds, STATUS LED will go from being continuously
lit to off.
3 − Continue to hold the short between R (2) to (1) beyond
ten seconds after STATUS LED has turned off. STATUS LED will turn on, indicating that error codes have
been cleared.
4 − Last ten error codes will be flashed on the STATUS
4 − Remove R (2) to (1) short. STATUS LED will flash to inLED.
dicate normal operation.
Page 6
II−Operation (all control boards)
A−Two Stage Operation / Thermostat
Selection
Electronic Ignition
At the beginning of each heating cycle, the SureLight® control monitors the first stage and second stage combustion
air inducer prove switch. The control will not begin the heating cycle if the first stage prove switch is closed
(by−passed). Likewise the control will not begin the second
stage heating cycle if the second stage prove switch is
closed, and will allow first stage heat only. However if the
second stage prove switch closes during the first stage pre−
purge, the control WILL respond to second stage heat call.
Once the first stage prove switch is determined to be open,
the combustion air inducer is energized on low (first stage)
heat speed. When the differential in the prove switch is
great enough, the prove switch closes and a 15−second
pre−purge begins. If the switch is not proven within 2−1/2
minutes, the control goes into Watchguard−Pressure
Switch mode for a 5−minute re−set period.
After the 15−second pre−purge period, the SureLight ignitor
warms up for 20 seconds after which the gas valve opens
for a 4−second trial for ignition. The ignitor energizes during
the trial until flame is sensed. If ignition is not proved during
the 4−second period, the control will try four more times with
an inter purge and warm−up time between trials of 35 seconds. After a total of five trials for ignition (including the
initial trial), the control goes into Watchguard−Flame Failure mode. After a 60−minute reset period, the control will
begin the ignition sequence again.
The SureLight control board has an added feature that prolongs the life of the ignitor. After a successful ignition,
boards 18M3401, 46M9901, 18M9901 and 49M5901 utilizes less power to energize the ignitor on successive calls
for heat. The boards continue to ramp down the voltage to
the ignitor until it finds the lowest amount of power that will
provide a successful ignition. This amount of power is used
for 255 cycles. On the 256th call for heat, the boards again
ramp down until the lowest power is determined and the
cycle begins again. SureLight boards 100869 and 100870
regulate 95 volts to the ignitor for consistent ignition and
long ignitor life.
SureLight Boards 18M3401, 46M9901, 18M9901 &
49M5901
Page 7
The control can be utilized in two modes: SINGLE−STAGE
thermostat or TWO−STAGE thermostat. The thermostat
selection jumper E20 must be positioned for the particular
application. The jumper is factory set on TWO" for use
with a two−stage thermostat with two stage heat. Re−position jumper to SINGLE" for use with a single stage
thermostat with two stage heat.
While in the single−stage thermostat mode (single jumper
setting), the burners will always fire on first−stage heat. The
combustion air inducer will operate on low speed and indoor blower will operate on low heat speed. After a field
selectable 10 or 15 minute delay (dip switch 3), the unit will
switch to second stage heat. While in the two−stage thermostat mode (two jumper setting) the burners will fire on
first−stage heat. The combustion air inducer will operate on
low speed and indoor blower will operate on low heat
speed. The unit will switch to second−stage heat on call
from the indoor thermostat. If there is a simultaneous call
for W1 and W2 (first and second stage heat) the unit will fire
on first stage heat and switch to second stage heat after 30
seconds of operation. See Sequence of Operation flow
charts in the back of this manual for more detail.
SureLight Boards 100869 & 100870
The control can be utilized in two modes: SINGLE−STAGE
thermostat or TWO−STAGE thermostat. The thermostat
selection is made using a dip switch (figure 2 ) and must be
positioned for the particular application. The dip switch is
factory set on TWO" for use with a two−stage thermostat
with two stage heat. Re−position dip switch to SINGLE" for
use with a single stage thermostat with two stage heat.
While in the single−stage thermostat mode (single dip
switch setting), the burners will always fire on first−stage
heat. The combustion air inducer will operate on low speed
and indoor blower will operate on low heat speed. After a
10 minute recognition period, the unit will switch to second
stage heat. While in the two−stage thermostat mode (two
dip switch setting) the burners will fire on first−stage heat.
The combustion air inducer will operate on low speed and
indoor blower will operate on low heat speed. The unit will
switch to second−stage heat on call from the indoor thermostat. If there is a simultaneous call for first and second stage
heat, the unit will fire an first stage heat and switch to second stage heat after 30 seconds of operation. See
Sequence of Operation flow charts in the back of this
manual for more detail.
Diagnostic LED’s (DS1 and DS2)
Two diagnostic LED’S are located on the two−stage integrated control board. See figure 1 . These light flashes
correspond with the codes detailed in table 5.
B−Dip Switch Settings
SureLight Boards 18M3401 & 46M9901
Dip Switches 1 and 2 − Heating Fan off Delay − The fan on
time of 45 seconds is not adjustable. Fan off time (time that
the blower operates after the heat demand has been satisfied) can be adjusted by flipping the dip switches 1 and 2
located on the SureLight integrated control. The unit is
shipped with a factory fan off setting of 90 seconds. Fan off
time will affect comfort and is adjustable to satisfy individual
applications. For customized comfort, monitor the supply
air temperature once the heat demand is satisfied. Note the
supply air temperature at the instant the blower is de−energized. Adjust the fan−off delay to achieve a supply air
temperature between 90° − 110° at the instant the blower is
de−energized. (Longer delay times allow for lower air temperature, shorter delay times allow for higher air
temperature). See table 8 for dip switch settings.
TABLE 8
Heating Fan Off Delay
Delay (Seconds)
Switch 1
Switch 2
60
90
120
180
Off
Off
On
On
Off
On
Off
On
Switch 3 − Second Stage Delay (Used with Single−Stage
Thermostat Only) −− This switch is used to determine the
second stage on delay when a single−stage thermostat is
being used. The switch is factory−set in the ON position,
which provides a 10−minute delay before second−stage
heat is initiated. If the switch is toggled to the OFF position,
it will provide a 15−minute delay before second−stage heat
is initiated. This switch is only activated when the thermostat selector jumper is positioned for SINGLE−stage
thermostat use.
Switch 4 − Cooling Fan off Delay − The fan on delay time
of 2 seconds is not adjustable. Fan off time (time that the
blower operates after the cool demand has been satisfied)
can be adjusted by flipping dip switch 4. The unit is shipped
with a factory fan off setting of 45 seconds. Fan off time will
affect comfort and is adjustable to satisfy individual applications. See table 9 for cool fan off time settings.
TABLE 9
Cooling Fan Off Delay
Delay (Seconds)
Switch 4
2
Off
45
On
Page 8
On−Board Jumper W915
A factory−installed jumper from Y1 to Y2 terminals on the
integrated control board terminal strip must be removed for
two−stage cooling. On board 18M3401 remove the jumper,
on board 46M9901 clip the jumper.
SureLight® Board 100869
Switch 1 −− Thermostat Selection −− This unit may be used
with either a single−stage or two−stage thermostat. The
thermostat selection is made using a DIP switch which
must be properly positioned for the particular application.
TheDIP switch is factory−positioned for use with a two−
stage thermostat. If a single−stage thermostat is to be used,
the DIP switch must be repositioned.
a − Select OFF" for two−stage heating operation controlled by a two−stage heating thermostat (factory
setting);
b − Select ON" for two−stage heating operation controlled by a single−stage heating thermostat. This
setting provides a timed delay before second−stage
heat is initiated.
Switch 2 −− Second Stage Delay (Used with Single−
Stage Thermostat Only) −− This switch is used to
determine the second stage on delay when a single−stage
thermostat is being used. The switch is factory−set in the
OFF position, which provides a 10−minute delay before
second−stage heat is initiated. If the switch is toggled to the
ON position, it will provide a 15−minute delay before second−stage heat is initiated. This switch is only activated
when the thermostat selector jumper is positioned for
SINGLE−stage thermostat use.
Switches 3 and 4 −− Heating Blower−Off Delay −− The
heating blower−on delay of 45 seconds is not adjustable.
The heating blower−off delay (time that the blower operates
after the heating demand has been satisfied) can be adjusted by moving switches 3 and 4 on the integrated control
board. The unit is shipped from the factory with a heating
blower−off delay of 90 seconds. The heating blower off
delay affects comfort and is adjustable to satisfy individual
applications. Adjust the blower off delay to achieve a supply air temperature between 90° and 110°F at the exact
moment that the blower is de−energized. Longer off delay
settings provide lower supply air temperatures; shorter settings provide higher supply air temperatures.Table 10
provides the blower off timings that will result from different
switch settings.
TABLE 11
Heating Blower−Off Delay Switch Settings
Blower Off Delay
Switch 3
Switch 4
(Seconds)
60
Off
On
90
Off
Off
120
On
Off
180
On
On
Switch 5 −− Cooling Blower−Off Delay −− The cooling
blower−off delay (time that the blower operates after the
cooling demand has been satisfied) can be adjusted by
moving switch 5 on the integrated control board. The
switch is factory−set in the OFF position, which provides a
cooling blower−off delay of 45 seconds. If the switch is
toggled to the ON position, it will provide a 2−second cooling blower−off delay
On−Board Jumper W951
On−board jumper W951, which connects terminals R and O
on the integrated control board, must be cut when the furnace is installed in applications which include a heat pump
unit and a thermostat which features dual fuel use. If the
jumper is left intact, terminal O" will remain energized eliminating the HEAT MODE in the heat pump.
On−Board Jumper W915
On−board jumper W915, which connects terminals Y1 and
Y2 on the integrated control board, must be cut if two−stage
cooling will be used. If the jumper is not cut the outdoor unit
will operate in second−stage cooling only.
Variable Speed SureLight® Board 18M9901 &
49M5901
Dip Switch Settings
Switches 1 and 2 − Blower Off Delay The blower−on delay
of 45 seconds is not adjustable. The blower−off delay (time
that the blower operates after the heating demand has
been satisfied) can be adjusted by moving switches 1 and 2
on the integrated control board. The unit is shipped from
the factory with a blower−off delay of 90 seconds. The
blower off delay affects comfort and is adjustable to satisfy
individual applications. Adjust the blower off delay to
achieve a supply air temperature between 90° and 110°F at
the exact moment that the blower is de−energized. Longer
off delay settings provide lower supply air temperatures;
shorter settings provide higher supply air temperatures.
The table below provides the blower off timings that will result from different switch settings.
TABLE 12
Blower Off Delay Switch Settings
Blower Off Delay
Switch 1
Switch 2
(Seconds)
60
Off
Off
90
Off
On
120
On
Off
180
On
On
Page 9
Switch 3 − Second Stage Delay (Used with Single−Stage
Thermostat Only) This switch is used to determine the
second stage on delay when a single−stage thermostat is
being used. The switch is factory−set in the ON position,
which provides a 10−minute delay before second−stage
heat is initiated. If the switch is toggled to the OFF position,
it will provide a 15−minute delay before second−stage heat
is initiated. This switch is only activated when the thermostat selector jumper is positioned for SINGLE−stage
thermostat use.
Switch 4 − Not used
Switches 5 and 6 − Cooling Mode Blower Speed
Switches 5 and 6 are used to select cooling blower motor
speed. The unit is shipped from the factory with the dip
switches positioned for high speed (4) indoor blower motor
operation during the cooling mode. Table 13 provides the
cooling mode blower speeds that will result from different
switch settings.
TABLE 13
Cooling Mode Blower Speeds
Speed
1 − Low
2 − Medium Low
3 − Medium High
4 − High (Factory)
Switch 5
On
Off
On
Off
Switch 6
On
On
Off
Off
Switches 7 and 8 − Blower Speed Adjustment Switches
7 and 8 are used to select blower speed adjustment settings. The unit is shipped from the factory with the dip
switches positioned for NORMAL (no) adjustment. The dip
switches may be positioned to adjust the blower speed by
+10% or −10% to better suit the application. Table 14 provides blower speed adjustments that will result from
different switch settings.
TABLE 14
Blower Speed Adjustment
Adjustment
+10% (approx.)
NORMAL (Factory)
−10% (approx.)
Switch 7
On
Off
Off
Switch 8
Off
Off
On
Switches 9 and 10 − Cooling Mode Blower Speed Ramping −− Switches 9 and 10 are used to select cooling mode
blower speed ramping options. Blower speed ramping may
be used to enhance dehumidification performance. The
switches are factory set at option A which has the greatest
effect on blower motor performance. Table 15 provides the
cooling mode blower speed ramping options that will result
from different switch settings. The cooling mode blower
speed ramping options are detailed on Page 12.
TABLE 15
Cooling Mode Blower Speed Ramping
Ramping Option
Switch 9
Switch 10
A (Factory)
Off
Off
B
On
Off
C
Off
On
D*
On
On
*Only option for Dehumidificaion
Switches 11 and 12 − Heating Mode Blower Speed
Switches 11 and 12 are used to select heating mode blower
motor speed. The unit is shipped from the factory with the
dip switches positioned for medium low (2) speed indoor
blower motor operation during the heating mode. Table 16
provides the heating mode blower speeds that will result
from different switch settings.
TABLE 16
Heating Mode Blower Speeds
Speed
Switch 11
Switch 12
1 − Low
On
On
2 − Medium Low
Off
On
(Factory)
3 − Medium High
On
Off
4 − High
Off
Off
Page 10
On−Board Jumper W914
On−board jumper W914, which connects terminals DS and
R on the integrated control board, must be cut when the furnace is installed with either the Harmony II zone control
board or a humidity control. Refer to furnace Installation Instructions for more detail.
On Board Jumper W915
A factory−installed jumper from Y1 to Y2 terminals on the
integrated control board terminal strip must be removed for
two−stage cooling. On board 18M9901 remove the jumper,
on board 49M5901 clip the jumper.
On−Board Jumper W951
On−board jumper W951, which connects terminals R and O
on the integrated control board, must be cut when the furnace is installed in applications which include a heat pump
unit and the FM21 FuelMaster control board.
Diagnostic LEDs (DS1 and DS2)
Two diagnostic LEDs are located on the two−stage, variable speed integrated control just to the left of the first bank
of dip switches. These lights’ flashes correspond with diagnostic codes detailed in table 5.
Status LEDs (HEAT, HI/LO, ON/OFF and CFM)
The integrated control includes four LEDs which indicate
operating status. The green ON/OFF LED is lit any time the
blower is operating. The green CFM LED indicates the
blower motor speed. Count the number of blinks between
the two−second pauses to determine the CFM. Each blink
represents approximately 100 CFM. The yellow HI/LO LED
is lit when the W914 (DS to R) jumper has not been clipped
for CCB1 or Harmony operation. The yellow HEAT LED is
lit when the indoor blower is operating at the HEATING
speed.
Variable Speed SureLight® Board 100870
Heating Operation DIP Switch Settings
Switch 1 −− Thermostat Selection −− This unit may be used
with either a single−stage or two−stage thermostat. The
thermostat selection is made using a DIP switch which
must be properly positioned for the particular application.
TheDIP switch is factory−positioned for use with a two−
stage thermostat. If a single−stage thermostat is to be used,
the DIP switch must be repositioned.
a − Select OFF" for two−stage heating operation controlled by a two−stage heating thermostat (factory
setting);
b − Select ON" for two−stage heating operation controlled by a single−stage heating thermostat. This
setting provides a timed delay before second−stage
heat is initiated.
Switch 2 −− Second Stage Delay (Used with Single−
Stage Thermostat Only) −− This switch is used to
determine the second stage on delay when a single−stage
thermostat is being used. The switch is factory−set in the
OFF position, which provides a 10−minute delay before
second−stage heat is initiated. If the switch is toggled to the
ON position, it will provide a 15−minute delay before second−stage heat is initiated. This switch is only activated
when the thermostat selector jumper is positioned for
SINGLE−stage thermostat use.
Switches 3 and 4 −− Blower−Off Delay −− The blower−on
delay of 45 seconds is not adjustable. The blower−off delay
(time that the blower operates after the heating demand
has been satisfied) can be adjusted by moving switches 3
and 4 on the integrated control board. The unit is shipped
from the factory with a blower−off delay of 90 seconds. The
blower off delay affects comfort and is adjustable to satisfy
individual applications. Adjust the blower off delay to
achieve a supply air temperature between 90° and 110°F at
the exact moment that the blower is de−energized. Longer
off delay settings provide lower supply air temperatures;
shorter settings provide higher supply air temperatures.Table 17 provides the blower off timings that will result
from different switch settings.
Page 11
TABLE 17
Blower Off Delay Switch Settings
Blower Off Delay
(Seconds)
60
90
120
180
Switch 3
Switch 4
Off
Off
On
On
On
Off
Off
On
Indoor Blower Operation DIP Switch Settings
Switches 5 and 6 −− Cooling Mode Blower Speed −−
Switches 5 and 6 are used to select cooling blower motor
speed. The unit is shipped from the factory with the DIP
switches positioned for high speed (4) indoor blower motor
operation during the cooling mode. The table below provides the cooling mode blower speeds that will result from
different switch settings.
TABLE 18
Cooling Mode Blower Speeds
Speed
1 − Low
2 − Medium Low
3 − Medium High
4 − High (Factory)
Switch 5
On
Off
On
Off
Switch 6
On
On
Off
Off
Switches 7 and 8 −− Blower Speed Adjustment −−
Switches 7 and 8 are used to select blower speed adjustment settings. The unit is shipped from the factory with the
DIP switches positioned for NORMAL (no) adjustment.
The DIP switches may be positioned to adjust the blower
speed by +10% or −10% to better suit the application. The
table below provides blower speed adjustments that will result from different switch settings.
TABLE 19
Blower Speed Adjustment
Adjustment
+10% (approx.)
NORMAL (Factory)
−10% (approx.)
Switch 7
On
Off
Off
Switch 8
Off
Off
On
Switches 9 and 10 −− Cooling Mode Blower Speed
Ramping −− Switches 9 and 10 are used to select cooling
mode blower speed ramping options. Blower speed ramping may be used to enhance dehumidification
performance. The switches are factory set at option A
which has the greatest effect on blower motor performance. Table 20 provides the cooling mode blower speed
ramping options that will result from different switch settings. The cooling mode blower speed ramping options are
detailed on Page 12 .
NOTE − The off portion of the selected ramp profile also applies during heat pump operation in dual fuel applications.
TABLE 20
Cooling Mode Blower Speed Ramping
Ramping Option
Switch 9
Switch 10
A (Factory)
Off
Off
B
On
Off
C
Off
On
D
On
On
Switches 11 and 12 −− Heating Mode Blower Speed −−
Switches 11 and 12 are used to select heating mode blower
motor speed. The unit is shipped from the factory with the
dip switches positioned for medium low (2) speed indoor
blower motor operation during the heating mode. The table
below provides the heating mode blower speeds that will
result from different switch settings.
TABLE 21
Heating Mode Blower Speeds
Switch 11
Switch 12
Speed
1 − Low
On
On
2 − Medium Low
Off
On
(Factory)
3 − Medium High
On
Off
4 − High
Off
Off
On−Board Jumper W914
On−board jumper W914, which connects terminals DS and
R on the integrated control board, must be cut when the furnace is installed with either the Harmony III zone control
board or a thermostat which features humidity control. If
the jumper is left intact the PWM signal from the HARMONY III control will be blocked and also lead to control
damage.
On−Board Jumper W951
On−board jumper W951, which connects terminals R and O
on the integrated control board, must be cut when the furnace is installed in applications which include a heat pump
unit and a thermostat which features dual fuel use. If the
jumper is left intact, terminal O" will remain energized eliminating the HEAT MODE in the heat pump.
On−Board Jumper W915
On−board jumper W915, which connects terminals Y1 and
Y2 on the integrated control board, must be cut if two−stage
cooling will be used. If the jumper is not cut the outdoor unit
will operate in second−stage cooling only.
Status LEDs (SPEED, CFM, E−COM)1
The green SPEED LED indicates circulating blower speed
in response to the DS signal. The LED is lit during normal
blower operation and is off during a dehumidification demand. In Harmony III applications, the brightness of the
LED indicates the requested blower speed.
The green CFM LED indicates the blower air flow. Count
the number of blinks between the two−second pauses to
determine the CFM. Each blink represents approximately
100 CFM.
The green E−COM LED indicates that the control is receiving and processing of commands and inputs. The LED may
flash rapidly or may display a single flash, depending upon
the activity.
Page 12
S
S
S
S
Ramping Option A (Factory Selection)10−
Motor runs at 50% for 30 seconds.
Motor then runs at 82% for approximately
7−1/2 minutes.
If demand has not been satisfied after 7−1/2 minutes.
Motor runs at 100% until demand is satisfied.
Once demand is met, motor runs at 50% for 30 seconds then ramps down to stop.
7 1/2 MIN
82% CFM
OFF
100%
CFM
1/2 MIN
50% CFM
OFF
1/2 MIN
50% CFM
COOLING DEMAND
S
S
Ramping Option B
Motor runs at 82% for approximately 7−1/2 minutes. If
demand has not been satisfied after 7−1/2 minutes
motor runs at 100% until demand is satisfied.
Once demand is met, motor ramps down to stop.
7 1/2 MIN
82%CFM
OFF
100% CFM
OFF
COOLING DEMAND
S
S
Ramping Option C
Motor runs at 100% until demand is satisfied.
Once demand is met, motor runs at 100% for 45* seconds then ramps down to stop.
100% CFM
OFF
OFF
COOLING DEMAND
* G60UHV units date coded prior to 2−2006 will delay 60 seconds
Ramping Option D
S− Motor runs at 100% until demand is satisfied.
S− Once demand is met, motor ramps down to stop.
OFF
100% CFM
OFF
COOLING
DEMAND
OFF
100% CFM
COOLING
DEMAND
OFF
III−Additional Components
Ignitor
Flame Sensor
SureLight®
ignitors are made of durable silicon nitride. Ignitor longevity is enhanced by controlling voltage to the
ignitor. SureLight boards 18M3401, 46M9901, 18M9901
and 49M5901 finds the lowest ignitor temperature which
will successfully light the burner. SureLight boards 100869
and 100870 regulate 95 volts to the ignitor. Due to this feature of the boards, voltage cannot be measured so ignitor
must be ohmed. See table 22 for Ohm values and figure 3
for ignitor location.
NOTE − Electronic components are polarity sensitive.
Make sure that the furnace is wired correctly and is
properly grounded.
A flame sensor is located on the left side of the burner support. See figure 4 . The sensor is mounted on the flame
rollout plate and the tip protrudes into the flame envelope of
the left−most burner. The sensor can be removed for service without removing any part of the burners. During
operation, flame is sensed by current passed through the
flame and sensing electrode. The SureLight control allows
the gas valve to remain open as long as flame signal is
sensed. See table 23 for flame signal.
Sensor Location
(all boards)
FLAME ROLLOUT PLATE
SureLight Boards 18M3401, 46M9901, 18M9901,
49M5901 Ignitor Location
5/8"
MEASUREMENT IS TO I.D.
OF RETENTION RING
5/16"
13/32’
SENSOR
FIGURE 4
TABLE 23
Flame Signal in Microamps
BRACKET
IGNITOR
SureLight Boards 100869, 100870
Ignitor Location
5/8
"
MEASUREMENT IS TO
I.D. OF RETENTION
RING
7/32’
BRACKET
IGNITOR
BURNERS FRONT VIEW
FIGURE 3
TABLE 22
SureLight Board
Ohm Value
18M3401
46M9901
18M9901
49M5901
10.9 − 19.7
100869
100870
25 − 47
Page 13
SureLight
Board
Normal
Low
Drop Out
18M3401
46M9901
18M9901
49M5901
0.23
0.22
0.16
100869
100870
1.50
1.40
0.20
IV−Wiring Diagrams and Sequence of Operation
A−G60DF with SureLight® Board 18M3401 or 46M9901
Page 14
Sequence of Operation
Sequence depends on type thermostat used. Units are
applicable for single stage or two stage thermostats.
Both type thermostats are described below. Thermostat jumper E20 dictates which mode unit will operate
in. See flow chart for more sequence detail.
SureLight® Control Self Check
When there is a call for heat, the SureLight integrated control runs a self check. The control checks for S10 primary
limit, S21 secondary limit (s) and S47 rollout switch normally closed contacts. The control also checks for S102
high heat and S128 low heat prove switch normally open
contacts. Once self check is complete and all safety
switches are operational, heat call can continue.
Two−Stage Thermostat, Two Stage Heat. Jumper E20
set at TWO".
1− SureLight® control energizes combustion air inducer
B6 on low heat speed. Combustion air inducer runs
until S128 low heat prove switch contacts close (switch
must close within 2 1/2 minutes or control goes into
Watchguard Pressure Switch mode. High heat prove
switch S102 may also close). A 15 second pre−purge
follows once S128 closes.
2− SureLight control begins 20 second ignitor warm up
period.
3− Gas valve opens on first stage for a 4 second trial for
ignition. Ignitor stays energized during the trial or until
flame sensed.
4− Flame is sensed, gas valve remains on first stage heat,
ignitor de−energizes.
5− After 45 second delay, indoor blower B3 is energized
on low heat speed.
The furnace will stay in this mode until first stage demand is satisfied OR a second stage heat demand is
initiated.
6− Second stage heat demand initiated. A 30 second,
second stage recognition period begins.
7− The combustion air inducer ramps up to high heat
speed.
8− S102 high heat prove switch closes and the gas valve
energizes second stage heat.
9− B3 indoor blower ramps up to high heat speed.
Page 15
Single−Stage Thermostat, Two Stage Heat. Jumper
E20 set at SINGLE"
1− SureLight control energizes combustion air inducer B6
on low heat speed. Combustion air inducer runs until
S128 low heat prove switch contacts close (switch
must close within 2 1/2 minutes or control goes into
Watchguard Pressure Switch mode. High heat prove
switch S102 may also close). A 15 second pre−purge
follows once S128 closes.
2− SureLight control begins 20 second ignitor warm up
period.
3− Gas valve opens on first stage for a 4 second trial for
ignition. Ignitor stays energized during the trial or until
flame sensed.
4− Flame is sensed, gas valve remains on first stage heat,
ignitor de−energizes.
5− After 45 second delay, indoor blower B3 is energized
on low heat speed.
6− A 10 minute (factory set) or 15 minute (field set) second
stage heat delay period begins.
7− The combustion air inducer ramps up to high heat
speed.
8− S102 high heat prove switch closes and the gas valve
energizes second stage heat.
9− B3 indoor blower ramps up to high heat speed.
B−G60UH with SureLigth® Board 100869
Page 16
Sequence of Operation.
Sequence depends on type thermostat used. G60UH
units are applicable for single stage or two stage thermostats. Both type thermostats are described below.
Thermostat dip switch selection dictates which mode
unit will operate in. See flow chart for more sequence
detail.
SureLight® Control Self Check
When there is a call for heat, the SureLight integrated control runs a self check. The control checks for S10 primary
limit, S21 secondary limit (s) and S47 rollout switch normally closed contacts. The control also checks for S102
high heat and S128 low heat prove switch normally open
contacts. Once self check is complete and all safety
switches are operational, heat call can continue.
Two−Stage Thermostat, Two Stage Heat. Dip Switch
set at TWO".
1− SureLight control energizes combustion air inducer B6
on low heat speed. Combustion air inducer runs until
S128 low heat prove switch contacts close (switch
must close within 2 1/2 minutes or control goes into
Watchguard Pressure Switch mode. High heat prove
switch S102 may also close). A 15 second pre−purge
follows once S128 closes.
2− SureLight control begins 20 second ignitor warm up
period.
3− Gas valve opens on first stage for a 4 second trial for
ignition. Ignitor stays energized during the trial or until
flame sensed.
4− Flame is sensed, gas valve remains on first stage heat,
ignitor de−energizes.
5− After 45 second delay, indoor blower B3 is energized
on low heat speed.
The furnace will stay in this mode until first stage demand is satisfied OR a second stage heat demand is
initiated.
6− Second stage heat demand initiated. A 30 second second stage recognition period begins.
7− The combustion air inducer ramps up to high heat
speed.
8− S102 high heat prove switch closes and the gas valve
energizes second stage heat.
9− B3 indoor blower energizes on high heat speed.
Page 17
Single−Stage Thermostat, Two Stage Heat. Dip
Switch set at SINGLE"
1− SureLight control energizes combustion air inducer B6
on low heat speed. Combustion air inducer runs until
S128 low heat prove switch contacts close (switch
must close within 2 1/2 minutes or control goes into
Watchguard Pressure Switch mode. High heat prove
switch S102 may also close). A 15 second pre−purge
follows once S128 closes.
2− SureLight control begins 20 second ignitor warm up
period.
3− Gas valve opens on first stage for a 4 second trial for
ignition. Ignitor stays energized during the trial or until
flame sensed.
4− Flame is sensed, gas valve remains on first stage heat,
ignitor de−energizes.
5− After 45 second delay, indoor blower B3 is energized
on low heat speed.
6− A 10 minute (factory set) or 15 minute (field set) second
stage heat delay period begins.
7− After the delay the combustion air inducer ramps up to
high heat speed.
8− S102 high heat prove switch closes and the gas valve
energizes second stage heat.
9− B3 indoor blower energizes on high heat speed.
C−G60DFV with SureLight® Board 18M9901 or 49M5901
Page 18
Sequence of Operation
Sequence depends on type thermostat used.
G60UDFV units are applicable for single stage or two
stage thermostats. Both type thermostats are described below. Thermostat jumper E20 dictates which
mode unit will operate in. See flow chart for more sequence detail.
SureLight® Control Self Check
When there is a call for heat, the SureLight integrated control runs a self check. The control checks for S10 primary
limit, S21 secondary limit (s) and S47 rollout switch normally closed contacts. The control also checks for S102
high heat and S128 low heat prove switch normally open
contacts. Once self check is complete and all safety
switches are operational, heat call can continue.
Two−Stage Thermostat, Two Stage Heat. Jumper E20
set at TWO".
10− SureLight control energizes combustion air inducer B6
on low heat speed. Combustion air inducer runs until
S128 low heat prove switch contacts close (switch
must close within 2 1/2 minutes or control goes into
Watchguard Pressure Switch mode. High heat prove
switch S102 may also close). A 15 second pre−purge
follows once S128 closes.
11− SureLight control begins 20 second ignitor warm up
period.
12− Gas valve opens on first stage for a 4 second trial for
ignition. Ignitor stays energized during the trial or until
flame sensed.
13− Flame is sensed, gas valve remains on first stage heat,
ignitor de−energizes.
14− After 45 second delay, indoor blower B3 is energized
on low heat speed.
The furnace will stay in this mode until first stage demand is satisfied OR a second stage heat demand is
initiated.
15− Second stage heat demand initiated. A 30 second second stage recognition period begins.
16− The combustion air inducer ramps up to high heat
speed.
17− S102 high heat prove switch closes and the gas valve
energizes second stage heat.
18− B3 indoor blower ramps up to high heat speed.
Page 19
Single−Stage Thermostat, Two Stage Heat. Jumper
E20 set at SINGLE"
1− SureLight control energizes combustion air inducer B6
on low heat speed. Combustion air inducer runs until
S128 low heat prove switch contacts close (switch
must close within 2 1/2 minutes or control goes into
Watchguard Pressure Switch mode. High heat prove
switch S102 may also close). A 15 second pre−purge
follows once S128 closes.
2− SureLight control begins 20 second ignitor warm up
period.
3− Gas valve opens on first stage for a 4 second trial for
ignition. Ignitor stays energized during the trial or until
flame sensed.
4− Flame is sensed, gas valve remains on first stage heat,
ignitor de−energizes.
5− After 45 second delay, indoor blower B3 is energized
on low heat speed.
6− A 10 minute (factory set) or 15 minute (field set) second
stage heat delay period begins.
7− After the delay the combustion air inducer ramps up to
high heat speed.
8− S102 high heat prove switch closes and the gas valve
energizes second stage heat.
9− B3 indoor blower ramps up to high heat speed.
D−G60UHV with SureLight® Board 100870
Page 20
Sequence of Operation.
Sequence depends on type thermostat used. G60UHV
units are applicable for single stage or two stage thermostats. Both type thermostats are described below.
Thermostat dip switch selection dictates which mode
unit will operate in. See flow chart for more sequence
detail.
SureLight® Control Self Check
When there is a call for heat, the SureLight integrated control runs a self check. The control checks for S10 primary
limit, S21 secondary limit (s) and S47 rollout switch normally closed contacts. The control also checks for S102
high heat and S128 low heat prove switch normally open
contacts. Once self check is complete and all safety
switches are operational, heat call can continue.
Two−Stage Thermostat, Two Stage Heat. Dip Switch
set at TWO".
10− SureLight control energizes combustion air inducer B6
on low heat speed. Combustion air inducer runs until
S128 low heat prove switch contacts close (switch
must close within 2 1/2 minutes or control goes into
Watchguard Pressure Switch mode. High heat prove
switch S102 may also close). A 15 second pre−purge
follows once S128 closes.
11− SureLight control begins 20 second ignitor warm up
period.
12− Gas valve opens on first stage for a 4 second trial for
ignition. Ignitor stays energized during the trial or until
flame sensed.
13− Flame is sensed, gas valve remains on first stage heat,
ignitor de−energizes.
14− After 45 second delay, indoor blower B3 is energized
on low heat speed.
The furnace will stay in this mode until first stage demand is satisfied OR a second stage heat demand is
initiated.
15− Second stage heat demand initiated. A 30 second second stage recognition period begins.
16− The combustion air inducer ramps up to high heat
speed.
17− S102 high heat prove switch closes and the gas valve
energizes second stage heat.
18− B3 indoor blower ramps up to high heat speed.
Page 21
Single−Stage Thermostat, Two Stage Heat. Dip
Switch set at SINGLE"
1− SureLight control energizes combustion air inducer B6
on low heat speed. Combustion air inducer runs until
S128 low heat prove switch contacts close (switch
must close within 2 1/2 minutes or control goes into
Watchguard Pressure Switch mode. High heat prove
switch S102 may also close). A 15 second pre−purge
follows once S128 closes.
2− SureLight control begins 20 second ignitor warm up
period.
3− Gas valve opens on first stage for a 4 second trial for
ignition. Ignitor stays energized during the trial or until
flame sensed.
4− Flame is sensed, gas valve remains on first stage heat,
ignitor de−energizes.
5− After 45 second delay, indoor blower B3 is energized
on low heat speed.
6− A 10 minute (factory set) or 15 minute (field set) second
stage heat delay period begins.
7− After the delay the combustion air inducer ramps up to
high heat speed.
8− S102 high heat prove switch closes and the gas valve
energizes second stage heat.
9− B3 indoor blower ramps up to high heat speed.
V−Troubleshooting Flow Charts
E− SureLight® Boards 18M3401 & 46M9901
HEATING SEQUENCE OF OPERATION
NORMAL AND ABNORMAL HEATING MODE
GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF. INDOOR BLOWER OFF. CHECK FOR
BROKEN IGNITOR OR OPEN IGNITER CIRCUIT.
DS1 AND DS2 ALTERNATING FAST FLASH.
POWER ON
CONTROL SELF−CHECK OKAY?
POLARITY OKAY?
NO
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF. (RESET CONTROL BY
TURNING MAIN POWER OFF.) DS1 ON, DS2 ON
POLARITY REVERSED.
DS1 −− FAST FLASH
DS2 −− SLOW FLASH
NO
YES
IS THERE A
PROPER GROUND?
NO
SIGNAL HOLDS UNTIL UNIT IS PROPERLY GROUNDED.
DS1 AND DS2 ALTERNATING FAST FLASH.
NO
SIGNAL HOLDS UNTIL VOLTAGE RISES ABOVE 75 VOLTS.
DS1 AND DS2 ALTERNATING FAST FLASH.
YES
IS VOLTAGE
ABOVE 75 VOLTS?
YES
BURNER OFF?
(CONTINUOUS FLAME CHECK)
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER ON HEATING SPEED.
DS1 SLOW FLASH, DS2 OFF.
NO
YES
A
NORMAL OPERATION:
DS 1 −− SIMULTANEOUS SLOW FLASH
DS 2 −− SIMULTANEOUS SLOW FLASH
NO
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER ON. HAS PRIMARY OR
YES
SECONDARY LIMIT RESET WITHIN 3 MINUTES?
DS1 SLOW FLASH, DS2 ON.
NO
B
THERMOSTAT CALLS FOR HEAT:
DS 1 −− SIMULTANEOUS FAST FLASH
DS 2 −− SIMULTANEOUS FAST FLASH
NO
60−MINUTE LIMIT WATCHGUARD MODE.
GAS VALVE OFF, COMBUSTION AIR INDUCER
OFF, INDOOR BLOWER OFF WITH DELAY.
DS1 AND DS2 ALTERNATING SLOW FLASH.
YES
PRIMARY AND SECONDARY LIMIT
SWITCHES CLOSED?
YES
ROLLOUT SWITCH CLOSED?
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
NO
HAS MANUAL ROLLOUT SWITCH(ES) BEEN
RESET (CLOSED) WITHIN 3 MINUTES?
DS1 SLOW FLASH, DS2 ON.
YES
NO
YES
FIRST (LOW) STAGE PRESSURE SWITCH
CONTACTS OPEN?
NO
YES
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF. CONTROL REMAINS UNTIL
PRESSURE SWITCH IS DETECTED OPEN.
DS1 OFF, DS2 SLOW FLASH.
SECOND (HIGH) STAGE PRESSURE SWITCH
CONTACTS OPEN?
NO
GAS VALVE OFF.
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF.
CONTROL WILL NOT ATTEMPT SECOND−STAGE
OPERATION DURING THIS HEAT DEMAND.
FIRST−STAGE OPERATION WILL BE ATTEMPTED.
DS1 OFF, DS2 FAST FLASH.
TWO−STAGE OR SINGLE−STAGE THERMOSTAT
CALL FOR HEAT
COMBUSTION AIR INDUCER ON LOW SPEED.
DS1 AND DS2 SIMULTANEOUS FAST FLASH
CONTINUED ON NEXT PAGE
Page 22
HEATING SEQUENCE OF OPERATION
CONTINUED
THERMOSTAT CALLS FOR HEAT
DS1 AND DS2 SIMULTANEOUS FAST FLASH
(Refer to box A on previous page)
NO
FIRST−STAGE (LOW FIRE) PRESSURE
SWITCH CLOSED WITHIN 2.5 MINUTES?
GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF. INDOOR BLOWER OFF. UNIT WILL RETRY
AFTER 5−MINUTE WAIT PERIOD.
DS1 OFF, DS2 SLOW FLASH.
YES
15−SECOND COMBUSTION AIR INDUCER
PRE−PURGE INITIATED BY CLOSED FIRST−STAGE
PRESSURE SWITCH (or 15 SECOND
INTER−PURGE PERIOD.)
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
IGNITOR WARM−UP (20 SECONDS)
DS1 AND DS2 SIMULTANEOUS FAST FLASH
IS VOLTAGE ABOVE 75 VOLTS?
NO
COMBUSTION AIR INDUCER OFF, IGNITER OFF.
SIGNAL HOLDS UNTIL VOLTAGE RISES ABOVE 75 VOLTS.
DS1 AND DS2 ALTERNATING FAST FLASH.
NO
COMBUSTION AIR INDUCER OFF, IGNITER OFF.
SIGNAL HOLDS UNTIL UNIT IS PROPERLY GROUNDED.
DS1 AND DS2 ALTERNATING FAST FLASH.
NO
COMBUSTION AIR INDUCER OFF, IGNITOR OFF.
SIGNAL HOLDS UNTIL IGNITOR IS REPLACED
OR RECONNECTED.
DS1 AND DS2 ALTERNATING FAST FLASH.
YES
IS THERE A PROPER GROUND?
IS IGNITOR INTACT AND CONNECTED?
YES
AT END OF IGNITOR 20 SECOND WARM UP
PERIOD, 4−SECOND TRIAL FOR IGNITION.
GAS VALVE OPENS, IGNITOR ENERGIZED DURING
4−SECOND TRIAL UNTIL FLAME SENSED.
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
YES
4−SECOND FLAME STABILIZATION PERIOD.
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
FLAME RECTIFICATION CURRENT CHECK
CAN FLAME BE PROVEN WITHIN 4
SECONDS AFTER GAS VALVE OPENS?
(u0.15 microamps)
GAS VALVE OFF. COMBUSTION AIR
INDUCER ON. INDOOR BLOWER OFF.
DS1 SLOW FLASH, DS2 FAST FLASHN.
HAS CONTROL FAILED TO SENSE
FLAME FOR FIVE CONSECUTIVE TRIES
DURING A SINGLE HEAT DEMAND?
NO
NO
YES
WATCHGUARD MODE. GAS VALVE OFF,
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF.
DS1 AND DS2 ALTERNATING SLOW FLASH.
IS 60−MINUTE RESET PERIOD COMPLETE?
YES
YES
FLAME PRESENT?
YES
NO
HAS CONTROL RESET IGNITION SEQUENCE
FOUR (4) TIMES?
DS1 SLOW FLASH, DS2 FAST FLASH.
CONTINUED ON NEXT PAGE
Page 23
NO
HEATING SEQUENCE OF OPERATION
CONTINUED
THERMOSTAT CALLS FOR HEAT.
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
SEE BOX A.
FLAME SIGNAL ABOVE
(u0.2 microamps)
NO
LOW FLAME SIGNAL
(Does not affect control operation)
DS1 SLOW FLASH, DS2 FAST FLASH.
YES
YES
SINGLE−STAGE THERMOSTAT MODE
(E20 SET AT SINGLE")
TWO STAGE THERMOSTAT MODE
(E20 SET AT TWO")
YES
YES
START SECOND−STAGE RECOGNITION
ON DELAY (10 OR 15 MINUTES).
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
45−SECOND INDOOR BLOWER ON DELAY BEGINS.
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
YES
YES
FIRST−STAGE (LOW FIRE)
PRESSURE SWITCH CLOSED?
YES
NO
NO
C
NO
PRIMARY AND SECONDARY LIMITS AND ROLLOUT
SWITCHES CLOSED?
GAS VALVE OFF, COMBUSTION AIR INDUCER OFF,
INDOOR BLOWER ON. DS1 SLOW FLASH, DS2 ON.
FIRST−STAGE HEAT DEMAND SATISFIED?
DS1 AND DS2 SIMULTANEOUS SLOW FLASH.
YES
GAS VALVE OFF, COMBUSTION AIR INDUCER
OFF FOLLOWING POST PURGE.
INDOOR BLOWER OFF WITH DELAY
DS1 AND DS2 SIMULTANEOUS SLOW FLASH
HAS PRIMARY, SECONDARY OR ROLLOUT
YES
SWITCH CLOSED WITHIN 3 MINUTES?
(Indoor blower on low speed during 3−minute period)
NO
SECOND−STAGE HEAT DEMAND.
SECOND−STAGE HEAT DEMAND REQUIRED?
DS1 AND DS2 SIMULTANEOUS SLOW FLASH.
LIMIT SWITCH WATCHGUARD MODE.
GAS VALVE OFF, COMBUSTION AIR INDUCER OFF,
YES
INDOOR BLOWER OFF WITH DELAY.
DS1 AND DS2 ALTERNATING SLOW FLASH.
IS 60−MINUTE RESET PERIOD COMPLETE?
YES
SECOND STAGE PRESSURE SWITCH CLOSED?
ABNORMAL FLASH CODE.
NOTE − IF SECOND−STAGE PRESSURE SWITCH
WAS ORIGINALLY FOUND CLOSED,
ABNORMAL CODE WILL FLASH.
YES
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF AFTER DELAY.
DS1 OFF, DS 2 SLOW FLASH.
NO
SECOND−STAGE PRESSURE SWITCH CLOSED
AT BEGINNING OF HEAT DEMAND?
DS1 OFF, DS2 SLOW FLASH.
SECOND−STAGE 30−SECOND DELAY ON BEGINS.
DS1 AND DS2 SIMULTANEOUS FAST FLASH
YES
SECOND STAGE HEAT DEMAND
DS1 AND DS2 SIMULTANEOUS SLOW FLASH.
SECOND−STAGE COMBUSTION AIR INDUCER
ON. SECOND−STAGE GAS VALVE ON. HIGH
HEAT INDOOR BLOWER SPEED ON.
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
NO
YES
SECOND−STAGE PRESSURE SWITCH CLOSED
IN LESS THAN TEN (10) SECONDS?
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
NO
RETURNS TO FIRST−STAGE HEAT MODE WHICH
CONTINUES UNTIL SECOND−STAGE PRESSURE
SWITCH CAN BE PROVEN or HEAT DEMAND IS
SATISFIED. FIVE (5) MINUTE WAIT PERIOD
INITIATED BEFORE RETRY. WERE 5 ATTEMPTS
MADE FOR SECOND−STAGE HEAT?
YES
YES
NORMAL OPERATION.
DS1 AND DS2 SIMULTANEOUS SLOW FLASH.
CONTINUED ON NEXT PAGE
Page 24
NO
HEATING SEQUENCE OF OPERATION
CONTINUED
SEE BOX A
NORMAL OPERATION
DS1 AND DS2 SIMULTANEOUS SLOW FLASH.
SEE BOX B
THERMOSTAT CALLS FOR HEAT
DS 1 AND DS 2 SIMULTANEOUS FAST FLASH
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER ON.
YES
DS1 SLOW FLASH, DS2 ON.
HAS PRIMARY, SECONDARY OR ROLLOUT
SWITCH CLOSED WITHIN 3 MINUTES?
NO
IS PRIMARY AND SECONDARY LIMIT
AND ROLLOUT SWITCH CLOSED?
YES
NO
LIMIT SWITCH WATCHGUARD MODE. GAS VALVE
OFF. COMBUSTION AIR INDUCER OFF. INDOOR
BLOWER OFF WITH DELAY. IS 60−MINUTE RESET
PERIOD COMPLETE? DS SLOW FLASH, DS2 ON.
GAS VALVE OFF, COMBUSTION AIR INDUCER OFF
AFTER 15 SECOND POST PURGE, INDOOR
YES
BLOWER OFF AFTER DELAY.
DS1 OFF, DS2 FAST FLASH.
RETURN TO HEAT DEMAND?
NO
FIRST−STAGE (LOW FIRE) HEAT
PRESSURE SWITCH CLOSED?
SECOND−STAGE (HIGH FIRE) HEAT
PRESSURE SWITCH CLOSED?
RETURN TO FIRST−STAGE HEAT MODE.
FIRST−STAGE CONTINUES UNTIL SECOND−
STAGE PRESSURE SWITCH CAN BE PROVEN
or HEAT DEMAND IS SATISFIED. A FIVE (5)
MINUTE WAIT PERIOD IS INITIATED BEFORE
RETRY. WERE 5 ATTEMPTS MADE FOR
SECOND−STAGE HEAT?
NO
SEE BOX C
FIRST−STAGE HEAT DEMAND SATISFIED?
NO
YES
HEAT DEMAND SATISFIED?
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
YES
SINGLE−STAGE THERMOSTAT MODE
(E20 SET AT SINGLE")
YES
YES
YES
TWO STAGE THERMOSTAT MODE?
(E20 SET AT TWO")
YES
YES
HEAT DEMAND SATISFIED?
DS1 AND DS2
SIMULTANEOUS FAST FLASH.
YES
FIRST AND SECOND STAGE HEAT
DEMAND SATISFIED SIMULTANEOUSLY.
DS1 & DS2 SIMULTANEOUS FAST FLASH.
NO
SECOND STAGE HEAT
DEMAND SATISFIED?
DS1 AND DS2
SIMULTANEOUS FAST FLASH.
YES
GAS VALVE OFF, COMBUSTION AIR
INDUCER OFF AFTER POST PURGE
PERIOD, INDOOR BLOWER OFF AFTER SELECTED DELAY.
DS1 AND DS2
SIMULTANEOUS FAST FLASH
YES
GAS VALVE, COMBUSTION AIR INDUCER
AND INDOOR BLOWER RETURN TO FIRST−
STAGE OPERATION.
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
FIRST STAGE HEAT DEMAND SATISFIED?
YES
GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF AFTER 5−SECOND POST−PURGE PERIOD.
INDOOR BLOWER OFF. DELAY INITIATED.
DS1 & DS2 SIMULTANEOUS FAST FLASH.
DEMAND FOR HEAT SATISFIED.
POWER ON STAND BY.
DS1 AND DS2
SIMULTANEOUS SLOW FLASH
Page 25
COOLING SEQUENCE OF OPERATION
POWER ON
YES
IS POLARITY REVERSED?
NO
YES
IS THERE
PROPER GROUND?
SIGNAL POLARITY REVERSED.
DS1 FAST FLASH, DS2 SLOW FLASH.
IS VOLTAGE
ABOVE 75 VOLTS?
YES
THERMOSTAT CALLS FOR FIRST−STAGE COOL.
COMPRESSOR AND CONDENSER FAN
ENERGIZED.
INDOOR BLOWER ENERGIZED ON FIRST−STAGE
COOL SPEED AFTER 2 SECOND DELAY.
FIRST−STAGE COOL DEMAND SATISFIED?
COMPRESSOR AND CONDENSER FAN DE−ENERGIZED.
INDOOR BLOWER DE−ENERGIZED AFTER
FIELD−SELECTED OFF DELAY.
YES
NO
THERMOSTAT CALLS FOR SECOND−STAGE COOL.
INDOOR BLOWER SWITCHES TO SECOND−STAGE COOL SPEED.
SECOND−STAGE COOL DEMAND SATISFIED?
YES
UNIT RETURNS TO FIRST−STAGE COOL
CONTINUOUS LOW SPEED FAN SEQUENCE OF OPERATION
NOTE − Continuous low speed fan and cooling low speed are equal to the low heat fan speed.
MANUAL FAN SELECTION MADE AT THERMOSTAT.
AFTER 2 SECOND DELAY, INDOOR BLOWER IS
ENERGIZED ON CONTINUOUS FAN SPEED
(LOW HEAT / LOW COOL).
YES
YES
THERMOSTAT CALLS FOR FIRST−STAGE COOL.
THERMOSTAT CALLS FOR FIRST−STAGE HEAT.
YES
YES
COMPRESSOR IS ENERGIZED AND INDOOR
BLOWER CONTINUES TO OPERATE IN LOW
COOL SPEED.
YES
BURNERS IGNITE AND INDOOR BLOWER
CONTINUES TO OPERATE IN CONTINUOUS
LOW (LOW HEAT / LOW COOL) MODE.
FIRST−STAGE COOL DEMAND SATISFIED?
FIRST−STAGE HEAT DEMAND SATISFIED.
NO
NO
SECOND−STAGE COOL DEMAND
THERMOSTAT CALLS FOR SECOND−STAGE HEAT.
INDOOR BLOWER SWITCHES TO
SECOND−STAGE COOL SPEED
INDOOR BLOWER SWITCHES TO HIGH HEAT SPEED
AFTER 30−SECOND RECOGNITION PERIOD.
YES
YES
SECOND−STAGE HEAT DEMAND SATISFIED.
SECOND−STAGE COOL DEMAND SATISFIED?
YES
YES
INDOOR BLOWER SWITCHES TO FIRST−STAGE
COOL SPEED.
INDOOR BLOWER SWITCHES TO LOW HEAT
SPEED.
Page 26
YES
F− SureLight Board® 100869
HEATING SEQUENCE OF OPERATION
NORMAL AND ABNORMAL HEATING MODE
POWER ON
CONTROL SELF−CHECK OKAY?
POLARITY OKAY?
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF. (RESET CONTROL BY
TURNING MAIN POWER OFF.)
NO
NO
POLARITY REVERSED.
STATUS ERROR CODE 5 + 4.
YES
IS THERE A
PROPER GROUND?
NO
SIGNAL HOLDS UNTIL UNIT IS PROPERLY GROUNDED.
STATUS ERROR CODE 5 + 3.
YES
A
NORMAL OPERATION:
STATUS LED −− PULSE
NO
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER ON. HAS PRIMARY OR
SECONDARY LIMIT RESET WITHIN 3 MINUTES? YES
STATUS ERROR CODE 3 + 1.
B
THERMOSTAT CALLS FOR HEAT:
STATUS LED −− HEARTBEAT
NO
NO
60−MINUTE LIMIT WATCHGUARD MODE.
GAS VALVE OFF, COMBUSTION AIR INDUCER
OFF, INDOOR BLOWER OFF WITH DELAY.
STATUS ERROR CODE 4 + 5.
YES
PRIMARY AND SECONDARY LIMIT
SWITCHES CLOSED?
YES
ROLLOUT SWITCH CLOSED?
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
NO
INDOOR BLOWER ON.
STATUS ERROR CODE 5 + 1.
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH IS YES
RESET AND MAIN POWER IS INTERRUPTED OR
T’STAT IS CYCLED OFF/ON FOR 3 SEC. MINIMUM.
NO
YES
FIRST (LOW) STAGE PRESSURE SWITCH
CONTACTS OPEN?
NO
YES
SECOND (HIGH) STAGE PRESSURE SWITCH
CONTACTS OPEN?
NO
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF. CONTROL REMAINS UNTIL
PRESSURE SWITCH IS DETECTED OPEN.
STATUS ERROR CODE 2 + 4
YES
GAS VALVE OFF.
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF.
CONTROL WILL NOT ATTEMPT SECOND−STAGE
OPERATION DURING THIS HEAT DEMAND.
FIRST−STAGE OPERATION WILL BE ATTEMPTED.
STATUS ERROR CODE 2 + 6.
TWO−STAGE OR SINGLE−STAGE THERMOSTAT
CALL FOR HEAT
COMBUSTION AIR INDUCER ON LOW SPEED.
STATUS LED −− HEARTBEAT
CONTINUED ON NEXT PAGE
Page 27
HEATING SEQUENCE OF OPERATION
CONTINUED
THERMOSTAT CALLS FOR HEAT
STATUS LED − HEARTBEAT.
(Refer to box A on previous page)
NO
FIRST−STAGE (LOW FIRE) PRESSURE
SWITCH CLOSED WITHIN 2.5 MINUTES?
GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF. INDOOR BLOWER OFF. UNIT WILL RETRY
AFTER 5−MINUTE WAIT PERIOD.
STATUS ERROR CODE 2 + 3.
YES
15−SECOND COMBUSTION AIR INDUCER
PRE−PURGE INITIATED BY CLOSED FIRST−STAGE
PRESSURE SWITCH (or 15 SECOND
INTER−PURGE PERIOD.)
STATUS LED −− HEARTBEAT.
IGNITOR WARM−UP (20 SECONDS)
STATUS LED −− HEARTBEAT.
YES
COMBUSTION AIR INDUCER OFF, IGNITOR OFF.
SIGNAL HOLDS UNTIL IGNITOR IS REPLACED
OR RECONNECTED.
STATUS ERROR CODE 4 + 7.
NO
IS IGNITOR INTACT AND CONNECTED?
YES
AT END OF IGNITOR 20 SECOND WARM UP
PERIOD, 4−SECOND TRIAL FOR IGNITION.
GAS VALVE OPENS, IGNITOR ENERGIZED DURING
4−SECOND TRIAL UNTIL FLAME SENSED.
IS VOLTAGE ABOVE 90 VOLTS?
YES
NO
YES
4−SECOND FLAME STABILIZATION PERIOD.
COMBUSTION AIR INDUCER OFF, IGNITER OFF.
SIGNAL HOLDS UNTIL VOLTAGE RISES ABOVE 95
VOLTS. STATUS ERROR CODE 4 + 8.
NO
FLAME RECTIFICATION CURRENT CHECK
CAN FLAME BE PROVEN WITHIN 4
SECONDS AFTER GAS VALVE OPENS?
(u0.20 microamps)
GAS VALVE OFF. COMBUSTION AIR
INDUCER ON. INDOOR BLOWER OFF.
STATUS LED −− HEARTBEAT.
HAS CONTROL FAILED TO SENSE
FLAME FOR FIVE CONSECUTIVE TRIES
DURING A SINGLE HEAT DEMAND?
NO
YES
WATCHGUARD MODE. GAS VALVE OFF,
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF.
STATUS ERROR CODE 4 + 1.
IS 60−MINUTE RESET PERIOD COMPLETE?
YES
YES
FLAME PRESENT?
YES
CONTINUED ON NEXT PAGE
NO
HAS CONTROL RESET IGNITION SEQUENCE
FOUR (4) TIMES?
WATCHGUARD MODE.
STATUS ERROR CODE 4 + 3.
Page 28
NO
HEATING SEQUENCE OF OPERATION
CONTINUED
THERMOSTAT CALLS FOR HEAT.
STATUS LED −− HEARTBEAT.
SEE BOX A.
FLAME SIGNAL ABOVE
(u1.40 microamps)
NO
LOW FLAME SIGNAL
(Does not affect control operation)
STATUS ERROR CODE 1 + 2.
YES
YES
SINGLE−STAGE THERMOSTAT MODE
(DIP SWITCH SET AT SINGLE")
TWO STAGE THERMOSTAT MODE
(DIP SWITCH SET AT TWO")
YES
YES
START SECOND−STAGE RECOGNITION
ON DELAY (10 OR 15 MINUTES).
STATUS LED −− HEARTBEAT
45−SECOND INDOOR BLOWER ON DELAY BEGINS.
STATUS LED −− HEARTBEAT.
YES
YES
ROLLOUT SWITCHES CLOSED?
PRIMARY & SECONDARY LIMIT SWITCHES
CLOSED?
NO
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER ON.
STATUS ERROR CODE 5 + 1. SEQUENCE HOLDS
UNTIL ROLLOUT SWITCH IS RESET AND MAIN
POWER IS INTERRUPTED OR THERMOSTAT
IS CYCLED OFF/ON FOR 3 SECOND MINIMUM.
YES
YES
FIRST−STAGE (LOW FIRE)
PRESSURE SWITCH CLOSED?
YES
NO
NO
NO
GAS VALVE OFF, COMBUSTION AIR INDUCER OFF,
INDOOR BLOWER ON.
STATUS ERROR CODE 3 + 1.
FIRST−STAGE HEAT DEMAND SATISFIED?
YES
GAS VALVE OFF, COMBUSTION AIR INDUCER
OFF FOLLOWING POST PURGE.
INDOOR BLOWER OFF WITH DELAY
STATUS LED −− PULSE
YES
HAS PRIMARY OR SECONDARY LIMIT
SWITCH CLOSED WITHIN 3 MINUTES?
(Indoor blower on low speed during 3−minute period)
SECOND−STAGE HEAT DEMAND.
SECOND−STAGE HEAT DEMAND REQUIRED?
LIMIT SWITCH WATCHGUARD MODE.
GAS VALVE OFF, COMBUSTION AIR INDUCER OFF,
INDOOR BLOWER OFF WITH DELAY.
YES
STATUS ERROR CODE 4 + 5
IS 60−MINUTE RESET PERIOD COMPLETE?
NO
YES
SECOND STAGE PRESSURE SWITCH CLOSED?
ABNORMAL FLASH CODE.
NOTE − IF SECOND−STAGE PRESSURE SWITCH
WAS ORIGINALLY FOUND CLOSED,
ABNORMAL CODE WILL FLASH.
YES
NO
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF AFTER DELAY.
STATUS ERROR CODE 2 + 3. CONTROL RESTARTS YES
IGNITION SEQUENCE IF PRESSURE SWITCH
CLOSES WITHIN 2−1/2 MINUTES.
SECOND−STAGE PRESSURE SWITCH CLOSED
AT BEGINNING OF HEAT DEMAND?
STATUS ERROR CODE 2 + 6.
SECOND−STAGE 30−SECOND DELAY ON BEGINS.
STATUS LED −− HEARTBEAT.
YES
SECOND−STAGE COMBUSTION AIR INDUCER
ON. SECOND−STAGE GAS VALVE ON. HIGH
HEAT INDOOR BLOWER SPEED ON.
STATUS LED −− HEARTBEAT.
YES
SECOND−STAGE PRESSURE SWITCH CLOSED
IN LESS THAN TEN (10) SECONDS?
STATUS LED −− HEARTBEAT
NO
SECOND STAGE HEAT DEMAND
STATUS LED −− HEARTBEAT.
NO
RETURNS TO FIRST−STAGE HEAT MODE WHICH
CONTINUES UNTIL SECOND−STAGE PRESSURE
SWITCH CAN BE PROVEN or HEAT DEMAND IS
SATISFIED. FIVE (5) MINUTE WAIT PERIOD
INITIATED BEFORE RETRY. WERE 5 ATTEMPTS
MADE FOR SECOND−STAGE HEAT?
YES
CONTINUES FIRST−STAGE HEATING DEMAND.
WILL NOT REATTEMPT SECOND−STAGE
HEATING DEMAND.
STATUS ERROR CODE 2 + 5.
YES
CONTINUED ON NEXT PAGE
Page 29
NO
HEATING SEQUENCE OF OPERATION
CONTINUED
SEE BOX A
NORMAL OPERATION.
SEE BOX B
THERMOSTAT CALLS FOR HEAT.
SECOND−STAGE (HIGH FIRE) HEAT
PRESSURE SWITCH CLOSED?
RETURN TO FIRST−STAGE HEAT MODE.
FIRST−STAGE CONTINUES UNTIL SECOND−
STAGE PRESSURE SWITCH CAN BE PROVEN
or HEAT DEMAND IS SATISFIED. A FIVE (5)
MINUTE WAIT PERIOD IS INITIATED BEFORE
RETRY. WERE 5 ATTEMPTS MADE FOR
SECOND−STAGE HEAT?
NO
SEE BOX C
FIRST−STAGE HEAT DEMAND SATISFIED?
NO
YES
HEAT DEMAND SATISFIED?
STATUS LED −− HEARTBEAT.
YES
YES
TWO STAGE THERMOSTAT MODE?
(DIP SWITCH SET AT TWO")
SINGLE−STAGE THERMOSTAT MODE
(DIP SWITCH SET AT SINGLE")
YES
YES
GAS VALVE OFF, COMBUSTION AIR
INDUCER OFF AFTER 5−SECOND
LOW SPEED POST PURGE PERIOD,
INDOOR BLOWER OFF DELAY
INITIATED ON LOW HEAT SPEED.
STATUS LED −− HEARTBEAT.
YES
YES
FIRST AND SECOND STAGE HEAT
DEMAND SATISFIED SIMULTANEOUSLY.
STATUS LED −− HEARTBEAT.
NO
SECOND STAGE HEAT
DEMAND SASTISFIED?
STATUS LED −− HEARTBEAT.
YES
GAS VALVE, COMBUSTION AIR INDUCER
AND INDOOR BLOWER RETURN TO FIRST−
STAGE OPERATION.
STATUS LED −− HEARTBEAT.
FIRST STAGE HEAT DEMAND SATISFIED?
YES
GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF AFTER 5−SECOND LOW SPEED POST−
PURGE PERIOD. INDOOR BLOWER OFF.
DELAY INITIATED ON LOW HEAT SPEED.
STATUS LED −− PULSE.
DEMAND FOR HEAT SATISFIED.
POWER ON STAND BY.
STATUS LED −− PULSE.
Page 30
COOLING SEQUENCE OF OPERATION
POWER ON
YES
IS POLARITY REVERSED?
SIGNAL POLARITY REVERSED.
CONTROL WILL CONTINUE TO CALL FOR COOLING
IN THIS CONDITION.
STATUS ERROR CODE 5 + 4.
NO
SIGNAL IMPROPER GROUND AT LED.
CONTROL WILL CONTINUE TO CALL FOR COOLING
IN THIS CONDITION.
STATUS ERROR CODE 5 + 3.
NO
IS THERE
PROPER GROUND?
YES
THERMOSTAT CALLS FOR FIRST−STAGE COOL.
COMPRESSOR AND CONDENSER FAN
ENERGIZED.
INDOOR BLOWER ENERGIZED ON FIRST STAGE
COOL SPEED AFTER 2 SECOND DELAY.
FIRST−STAGE DEMAND FOR COOL SATISFIED?
YES
NO
THERMOSTAT CALLS FOR SECOND−STAGE COOL.
INDOOR BLOWER RAMPS UP TO SECOND−STAGE COOL SPEED.
SECOND−STAGE DEMAND FOR COOL SATISFIED?
YES
UNIT RETURNS TO FIRST STAGE COOL
Page 31
COMPRESSOR AND CONDENSER FAN DE−ENERGIZED.
INDOOR BLOWER DE−ENEGIZED.
CONTINUOUS LOW SPEED FAN SEQUENCE OF OPERATION
MANUAL FAN SELECTION MADE AT THERMOSTAT.
AFTER 2 SECOND DELAY, INDOOR BLOWER IS
ENERGIZED ON CONTINUOUS FAN SPEED.
YES
YES
THERMOSTAT CALLS FOR FIRST STAGE COOL.
YES
YES
INDOOR BLOWER RAMPS TO FIRST STAGE
COOLING SPEED AFTER A 2−SECOND DELAY.
YES
THERMOSTAT CALLS FOR FIRST−STAGE HEAT.
AFTER 45−SECOND DELAY, INDOOR BLOWER
SWITCHES TO LOW HEAT SPEED.
FIRST−STAGE COOL DEMAND SATISFIED?
FIRST−STAGE HEAT DEMAND SATISFIED.
NO
NO
SECOND STAGE COOL DEMAND
THERMOSTAT CALLS FOR SECOND−STAGE HEAT.
YES
INDOOR BLOWER RAMPS TO SECOND
STAGE COOL SPEED
INDOOR BLOWER SWITCHES TO HIGH HEAT SPEED
AFTER 30−SECOND RECOGNITION PERIOD.
YES
SECOND STAGE COOL DEMAND SATISFIED?
SECOND−STAGE HEAT DEMAND SATISFIED.
YES
YES
INDOOR BLOWER RAMPS DOWN TO FIRST STAGE
COOL SPEED.
Page 32
INDOOR BLOWER RAMPS DOWN TO LOW
HEAT SPEED.
YES
G− SureLight® Variable SpeedBoard 18M9901 & 49M5901
HEATING SEQUENCE OF OPERATION
NORMAL AND ABNORMAL HEATING MODE
GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF. INDOOR BLOWER OFF. CHECK FOR
BROKEN IGNITOR OR OPEN IGNITER CIRCUIT.
DS 1 AND DS 2 ALTERNATING FAST FLASH.
POWER ON
CONTROL SELF−CHECK OKAY?
POLARITY OKAY?
NO
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF. (RESET CONTROL BY
TURNING MAIN POWER OFF.) DS1 ON, DS2 ON
POLARITY REVERSED.
DS 1 −− FAST FLASH
DS 2 −− SLOW FLASH
NO
YES
IS THERE A
PROPER GROUND?
NO
SIGNAL HOLDS UNTIL UNIT IS PROPERLY GROUNDED.
DS1 AND DS2 ALTERNATING FAST FLASH.
NO
SIGNAL HOLDS UNTIL VOLTAGE RISES ABOVE 75 VOLTS.
DS1 AND DS2 ALTERNATING FAST FLASH.
YES
IS VOLTAGE
ABOVE 75 VOLTS?
YES
BURNER OFF?
(CONTINUOUS FLAME CHECK)
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER ON HEATING SPEED.
DS1 SLOW FLASH, DS2 OFF,
ON/OFF LED OFF
NO
YES
A
NORMAL OPERATION:
DS 1 −− SIMULTANEOUS SLOW FLASH
DS 2 −− SIMULTANEOUS SLOW FLASH
NO
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER ON. HAS PRIMARY OR
SECONDARY LIMIT RESET WITHIN 3 MINUTES?
YES
DS1 SLOW FLASH, DS2 ON,
ON/OFF LED ON, HEAT LED ON.
B
THERMOSTAT CALLS FOR HEAT:
DS 1 −− SIMULTANEOUS FAST FLASH
DS 2 −− SIMULTANEOUS FAST FLASH
NO
NO
60−MINUTE LIMIT WATCHGUARD MODE.
GAS VALVE OFF, COMBUSTION AIR INDUCER
OFF, INDOOR BLOWER OFF WITH DELAY.
DS1 AND DS2 ALTERNATING SLOW FLASH,
ON/OFF LED OFF, HEAT LED ON.
YES
PRIMARY AND SECONDARY LIMIT
SWITCHES CLOSED?
YES
ROLLOUT SWITCH CLOSED?
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
NO
HAS MANUAL ROLLOUT SWITCH(ES) BEEN
RESET (CLOSED) WITHIN 3 MINUTES?
DS1 SLOW FLASH, DS2 ON,
YES
ON/OFF LED ON, HEAT LED ON.
NO
YES
FIRST (LOW) STAGE PRESSURE SWITCH
CONTACTS OPEN?
NO
YES
SECOND (HIGH) STAGE PRESSURE SWITCH
CONTACTS OPEN?
NO
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF. CONTROL REMAINS UNTIL
PRESSURE SWITCH IS DETECTED OPEN.
DS1 OFF, DS2 SLOW FLASH,
ON/OFF LED OFF, HEAT LED OFF.
GAS VALVE OFF.
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF.
CONTROL WILL NOT ATTEMPT SECOND−STAGE
OPERATION DURING THIS HEAT DEMAND.
FIRST−STAGE OPERATION WILL BE ATTEMPTED.
DS1 OFF, DS2 FAST FLASH,
ON/OFF LED OFF, HEAT LED ON.
TWO−STAGE OR SINGLE−STAGE THERMOSTAT
CALL FOR HEAT
COMBUSTION AIR INDUCER ON LOW SPEED.
DS1 AND DS2 SIMULTANEOUS FAST FLASH
CONTINUED ON NEXT PAGE
Page 33
HEATING SEQUENCE OF OPERATION
CONTINUED
THERMOSTAT CALLS FOR HEAT
DS1 AND DS2 SIMULTANEOUS FAST FLASH
(Refer to box A on previous page)
NO
FIRST−STAGE (LOW FIRE) PRESSURE
SWITCH CLOSED WITHIN 2.5 MINUTES?
GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF. INDOOR BLOWER OFF. UNIT WILL RETRY
AFTER 5−MINUTE WAIT PERIOD.
DS1 OFF, DS2 SLOW FLASH,
ON/OFF LED OFF, HEAT LED OFF.
YES
15−SECOND COMBUSTION AIR INDUCER
PRE−PURGE INITIATED BY CLOSED FIRST−STAGE
PRESSURE SWITCH (or 15 SECOND
INTER−PURGE PERIOD.)
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
IGNITOR WARM−UP (20 SECONDS)
DS1 AND DS2 SIMULTANEOUS FAST FLASH
IS VOLTAGE ABOVE 75 VOLTS?
NO
COMBUSTION AIR INDUCER OFF, IGNITER OFF.
SIGNAL HOLDS UNTIL VOLTAGE RISES ABOVE 75 VOLTS.
DS1 AND DS2 ALTERNATING FAST FLASH.
NO
COMBUSTION AIR INDUCER OFF, IGNITER OFF.
SIGNAL HOLDS UNTIL UNIT IS PROPERLY GROUNDED.
DS1 AND DS2 ALTERNATING FAST FLASH.
NO
COMBUSTION AIR INDUCER OFF, IGNITOR OFF.
SIGNAL HOLDS UNTIL IGNITOR IS REPLACED
OR RECONNECTED.
DS1 AND DS2 ALTERNATING FAST FLASH.
YES
IS THERE A PROPER GROUND?
IS IGNITOR INTACT AND CONNECTED?
YES
AT END OF IGNITOR 20 SECOND WARM UP
PERIOD, 4−SECOND TRIAL FOR IGNITION.
GAS VALVE OPENS, IGNITOR ENERGIZED DURING
4−SECOND TRIAL UNTIL FLAME SENSED.
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
YES
4−SECOND FLAME STABILIZATION PERIOD.
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
FLAME RECTIFICATION CURRENT CHECK
CAN FLAME BE PROVEN WITHIN 4
SECONDS AFTER GAS VALVE OPENS?
(u0.15 microamps)
GAS VALVE OFF. COMBUSTION AIR
INDUCER ON. INDOOR BLOWER OFF.
DS1 SLOW FLASH, DS2 FAST FLASH,
ON/OFF LED OFF, HEAT LED 0N.
HAS CONTROL FAILED TO SENSE
FLAME FOR FIVE CONSECUTIVE TRIES
DURING A SINGLE HEAT DEMAND?
NO
NO
YES
WATCHGUARD MODE. GAS VALVE OFF,
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF.
DS1 AND DS2 ALTERNATING SLOW FLASH.
ON/OFF LED 0FF, HEAT LED OFF.
IS 60−MINUTE RESET PERIOD COMPLETE?
YES
YES
FLAME PRESENT?
YES
CONTINUED ON NEXT PAGE
NO
HAS CONTROL RESET IGNITION SEQUENCE
FOUR (4) TIMES?
DS1 SLOW FLASH, DS2 FAST FLASH,
ON/OFF LED OFF, HEAT LED ON .
Page 34
NO
HEATING SEQUENCE OF OPERATION
CONTINUED
THERMOSTAT CALLS FOR HEAT.
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
SEE BOX A.
FLAME SIGNAL ABOVE
(u0.2 microamps)
NO
LOW FLAME SIGNAL
(Does not affect control operation)
DS1 SLOW FLASH, DS2 FAST FLASH.
YES
YES
SINGLE−STAGE THERMOSTAT MODE
(E20 SET AT SINGLE")
TWO STAGE THERMOSTAT MODE
(E20 SET AT TWO")
YES
YES
START SECOND−STAGE RECOGNITION
ON DELAY (10 OR 15 MINUTES).
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
45−SECOND INDOOR BLOWER ON DELAY BEGINS.
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
YES
YES
FIRST−STAGE (LOW FIRE)
PRESSURE SWITCH CLOSED?
YES
NO
NO
C
NO
PRIMARY AND SECONDARY LIMITS AND ROLLOUT
SWITCHES CLOSED?
GAS VALVE OFF, COMBUSTION AIR INDUCER OFF,
INDOOR BLOWER ON. DS1 SLOW FLASH, DS2 ON,
ON/OFF LED ON, HEAT LED ON.
FIRST−STAGE HEAT DEMAND SATISFIED?
DS1 AND DS2 SIMULTANEOUS SLOW FLASH.
YES
GAS VALVE OFF, COMBUSTION AIR INDUCER
OFF FOLLOWING POST PURGE.
INDOOR BLOWER OFF WITH DELAY
DS1 AND DS2 SIMULTANEOUS SLOW FLASH
HAS PRIMARY, SECONDARY OR ROLLOUT
YES
SWITCH CLOSED WITHIN 3 MINUTES?
(Indoor blower on low speed during 3−minute period)
NO
SECOND−STAGE HEAT DEMAND.
SECOND−STAGE HEAT DEMAND REQUIRED?
DS1 AND DS2 SIMULTANEOUS SLOW FLASH.
LIMIT SWITCH WATCHGUARD MODE.
GAS VALVE OFF, COMBUSTION AIR INDUCER OFF,
YES
INDOOR BLOWER OFF WITH DELAY.
DS1 AND DS2 ALTERNATING SLOW FLASH,
ON/OFF LED OFF, HEAT LED OFF.
IS 60−MINUTE RESET PERIOD COMPLETE?
YES
SECOND STAGE PRESSURE SWITCH CLOSED?
ABNORMAL FLASH CODE.
NOTE − IF SECOND−STAGE PRESSURE SWITCH
WAS ORIGINALLY FOUND CLOSED,
ABNORMAL CODE WILL FLASH.
YES
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF AFTER DELAY.
DS1 OFF, DS 2 SLOW FLASH,
ON/OFF LED OFF, HEAT LED ON.
NO
SECOND−STAGE PRESSURE SWITCH CLOSED
AT BEGINNING OF HEAT DEMAND?
DS1 OFF, DS2 SLOW FLASH,
ON/OFF LED ON, HEAT LED ON.
SECOND−STAGE 30−SECOND DELAY ON BEGINS.
DS1 AND DS2 SIMULTANEOUS FAST FLASH
YES
SECOND STAGE HEAT DEMAND
DS1 AND DS2 SIMULTANEOUS SLOW FLASH.
SECOND−STAGE COMBUSTION AIR INDUCER
ON. SECOND−STAGE GAS VALVE ON. HIGH
HEAT INDOOR BLOWER SPEED ON.
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
ON/OFF LED ON.
NO
YES
SECOND−STAGE PRESSURE SWITCH CLOSED
IN LESS THAN TEN (10) SECONDS?
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
NO
RETURNS TO FIRST−STAGE HEAT MODE WHICH
CONTINUES UNTIL SECOND−STAGE PRESSURE
SWITCH CAN BE PROVEN or HEAT DEMAND IS
SATISFIED. FIVE (5) MINUTE WAIT PERIOD
INITIATED BEFORE RETRY. WERE 5 ATTEMPTS
MADE FOR SECOND−STAGE HEAT?
YES
YES
NORMAL OPERATION.
DS1 AND DS2 SIMULTANEOUS SLOW FLASH.
CONTINUED ON NEXT PAGE
Page 35
NO
HEATING SEQUENCE OF OPERATION
CONTINUED
SEE BOX A
NORMAL OPERATION
DS1 AND DS2 SIMULTANEOUS SLOW FLASH.
SEE BOX B
THERMOSTAT CALLS FOR HEAT
DS 1 AND DS 2 SIMULTANEOUS FAST FLASH
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER ON.
YES
DS1 SLOW FLASH, DS2 ON,
ON/OFF LED ON, HEAT LED 0N.
HAS PRIMARY, SECONDARY OR ROLLOUT
SWITCH CLOSED WITHIN 3 MINUTES?
NO
IS PRIMARY AND SECONDARY LIMIT
AND ROLLOUT SWITCH CLOSED?
YES
NO
LIMIT SWITCH WATCHGUARD MODE. GAS VALVE
OFF. COMBUSTION AIR INDUCER OFF. INDOOR
BLOWER OFF WITH DELAY. IS 60−MINUTE RESET
PERIOD COMPLETE? DS SLOW FLASH, DS2 ON,
ON/OFF LED OFF, HEAT LED OFF.
GAS VALVE OFF, COMBUSTION AIR INDUCER OFF
AFTER 15 SECOND POST PURGE, INDOOR
YES
BLOWER OFF AFTER DELAY.
DS1 OFF, DS2 FAST FLASH,
ON/OFF LED ON, HEAT LED ON.
RETURN TO HEAT DEMAND?
NO
FIRST−STAGE (LOW FIRE) HEAT
PRESSURE SWITCH CLOSED?
SECOND−STAGE (HIGH FIRE) HEAT
PRESSURE SWITCH CLOSED?
RETURN TO FIRST−STAGE HEAT MODE.
FIRST−STAGE CONTINUES UNTIL SECOND−
STAGE PRESSURE SWITCH CAN BE PROVEN
or HEAT DEMAND IS SATISFIED. A FIVE (5)
MINUTE WAIT PERIOD IS INITIATED BEFORE
RETRY. WERE 5 ATTEMPTS MADE FOR
SECOND−STAGE HEAT?
NO
SEE BOX C
FIRST−STAGE HEAT DEMAND SATISFIED?
NO
YES
HEAT DEMAND SATISFIED?
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
YES
SINGLE−STAGE THERMOSTAT MODE
(E20 SET AT SINGLE")
YES
YES
YES
TWO STAGE THERMOSTAT MODE?
(E20 SET AT TWO")
YES
YES
HEAT DEMAND SATISFIED?
DS1 AND DS2
SIMULTANEOUS FAST FLASH.
YES
FIRST AND SECOND STAGE HEAT
DEMAND SATISFIED SIMULTANEOUSLY.
DS1 & DS2 SIMULTANEOUS FAST FLASH.
NO
SECOND STAGE HEAT
DEMAND SATISFIED?
DS1 AND DS2
SIMULTANEOUS FAST FLASH.
YES
GAS VALVE OFF, COMBUSTION AIR
INDUCER OFF AFTER 5−SECOND
LOW SPEED POST PURGE PERIOD,
INDOOR BLOWER OFF DELAY
INITIATED ON LOW HEAT SPEED.
DS1 AND DS2
SIMULTANEOUS FAST FLASH
YES
GAS VALVE, COMBUSTION AIR INDUCER
AND INDOOR BLOWER RETURN TO FIRST−
STAGE OPERATION.
DS1 AND DS2 SIMULTANEOUS FAST FLASH.
FIRST STAGE HEAT DEMAND SATISFIED?
YES
GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF AFTER 5−SECOND LOW SPEED POST−
PURGE PERIOD. INDOOR BLOWER OFF.
DELAY INITIATED ON LOW HEAT SPEED.
DS1 & DS2 SIMULTANEOUS FAST FLASH.
DEMAND FOR HEAT SATISFIED.
POWER ON STAND BY.
DS1 AND DS2
SIMULTANEOUS SLOW FLASH
Page 36
COOLING SEQUENCE OF OPERATION
POWER ON
YES
IS POLARITY REVERSED?
SIGNAL IMPROPER
GROUND AT DS.
SIGNAL HOLDS
UNTIL UNIT IS
PROPERLY
GROUNDED.
SIGNAL POLARITY REVERSED.
DS1 FAST FLASH, DS2 SLOW FLASH.
NO
NO
YES
IS THERE
PROPER GROUND?
IS VOLTAGE
ABOVE 75 VOLTS?
YES
NO
LOW VOLTAGE SIGNAL AT DS HOLDS
UNTIL VOLTAGE RISES ABOVE 75 VOLTS.
THERMOSTAT CALLS FOR FIRST−STAGE COOL.
COMPRESSOR AND CONDENSER FAN
ENERGIZED.
INDOOR BLOWER ENERGIZED ON FIRST−STAGE
COOL SPEED AFTER 2 SECOND DELAY.
FIRST−STAGE DEMAND FOR COOL SATISFIED?
YES
NO
THERMOSTAT CALLS FOR SECOND−STAGE COOL.
INDOOR BLOWER RAMPS UP TO SECOND−STAGE COOL SPEED.
SECOND−STAGE COOL DEMAND SATISFIED?
YES
UNIT RETURNS TO FIRST−STAGE COOL.
Page 37
COMPRESSOR AND CONDENSER FAN DE−ENERGIZED.
INDOOR BLOWER DE−ENERGIZED AFTER
FIELD−SELECTED BLOWER OFF DELAY.
CONTINUOUS LOW SPEED FAN SEQUENCE OF OPERATION
MANUAL FAN SELECTION MADE AT THERMOSTAT.
AFTER 2 SECOND DELAY, INDOOR BLOWER IS
ENERGIZED ON CONTINUOUS FAN SPEED.
YES
YES
THERMOSTAT CALLS FOR FIRST STAGE COOL.
YES
YES
INDOOR BLOWER RAMPS TO FIRST STAGE
COOLING SPEED AFTER A 2−SECOND DELAY.
YES
THERMOSTAT CALLS FOR FIRST−STAGE HEAT.
AFTER 45−SECOND DELAY, INDOOR BLOWER
SWITCHES TO LOW HEAT SPEED.
FIRST−STAGE COOL DEMAND SATISFIED?
FIRST−STAGE HEAT DEMAND SATISFIED.
NO
NO
SECOND STAGE COOL DEMAND
THERMOSTAT CALLS FOR SECOND−STAGE HEAT.
YES
INDOOR BLOWER RAMPS TO SECOND
STAGE COOL SPEED
INDOOR BLOWER SWITCHES TO HIGH HEAT SPEED
AFTER 30−SECOND RECOGNITION PERIOD.
YES
SECOND STAGE COOL DEMAND SATISFIED?
SECOND−STAGE HEAT DEMAND SATISFIED.
YES
YES
INDOOR BLOWER RAMPS DOWN TO FIRST STAGE
COOL SPEED.
Page 38
INDOOR BLOWER RAMPS DOWN TO LOW
HEAT SPEED.
YES
H− SureLight® Variable Speed Board 100870
HEATING SEQUENCE OF OPERATION
NORMAL AND ABNORMAL HEATING MODE
POWER ON
CONTROL SELF−CHECK OKAY?
POLARITY OKAY?
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF. (RESET CONTROL BY
TURNING MAIN POWER OFF.)
NO
POLARITY REVERSED.
STATUS ERROR CODE 5 + 4.
NO
YES
IS THERE A
PROPER GROUND?
NO
SIGNAL HOLDS UNTIL UNIT IS PROPERLY GROUNDED.
STATUS ERROR CODE 5 + 3.
YES
A
NORMAL OPERATION:
STATUS LED −− PULSE
NO
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER ON. HAS PRIMARY OR
SECONDARY LIMIT RESET WITHIN 3 MINUTES? YES
STATUS ERROR CODE 3 + 1.
B
THERMOSTAT CALLS FOR HEAT:
STATUS LED −− HEARTBEAT
NO
NO
60−MINUTE LIMIT WATCHGUARD MODE.
GAS VALVE OFF, COMBUSTION AIR INDUCER
OFF, INDOOR BLOWER OFF WITH DELAY.
STATUS ERROR CODE 4 + 5.
YES
PRIMARY AND SECONDARY LIMIT
SWITCHES CLOSED?
YES
ROLLOUT SWITCH CLOSED?
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
NO
INDOOR BLOWER ON.
STATUS ERROR CODE 5 + 1.
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH IS YES
RESET AND MAIN POWER IS INTERRUPTED OR
T’STAT IS CYCLED OFF/ON FOR 3 SEC. MINIMUM.
NO
YES
FIRST (LOW) STAGE PRESSURE SWITCH
CONTACTS OPEN?
NO
YES
SECOND (HIGH) STAGE PRESSURE SWITCH
CONTACTS OPEN?
NO
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF. CONTROL REMAINS UNTIL
PRESSURE SWITCH IS DETECTED OPEN.
STATUS ERROR CODE 2 + 4
YES
GAS VALVE OFF.
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF.
CONTROL WILL NOT ATTEMPT SECOND−STAGE
OPERATION DURING THIS HEAT DEMAND.
FIRST−STAGE OPERATION WILL BE ATTEMPTED.
STATUS ERROR CODE 2 + 6.
TWO−STAGE OR SINGLE−STAGE THERMOSTAT
CALL FOR HEAT
COMBUSTION AIR INDUCER ON LOW SPEED.
STATUS LED −− HEARTBEAT
CONTINUED ON NEXT PAGE
Page 39
HEATING SEQUENCE OF OPERATION
CONTINUED
THERMOSTAT CALLS FOR HEAT
STATUS LED − HEARTBEAT
(Refer to box A on previous page)
NO
FIRST−STAGE (LOW FIRE) PRESSURE
SWITCH CLOSED WITHIN 2.5 MINUTES?
GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF. INDOOR BLOWER OFF. UNIT WILL RETRY
AFTER 5−MINUTE WAIT PERIOD.
STATUS ERROR CODE 2 + 3.
YES
15−SECOND COMBUSTION AIR INDUCER
PRE−PURGE INITIATED BY CLOSED FIRST−STAGE
PRESSURE SWITCH (or 15 SECOND
INTER−PURGE PERIOD.)
STATUS LED −− HEARTBEAT.
IGNITOR WARM−UP (20 SECONDS)
STATUS LED −− HEARTBEAT.
YES
COMBUSTION AIR INDUCER OFF, IGNITOR OFF.
SIGNAL HOLDS UNTIL IGNITOR IS REPLACED
OR RECONNECTED.
STATUS ERROR CODE 4 + 7.
NO
IS IGNITOR INTACT AND CONNECTED?
YES
AT END OF IGNITOR 20 SECOND WARM UP
PERIOD, 4−SECOND TRIAL FOR IGNITION.
GAS VALVE OPENS, IGNITOR ENERGIZED DURING
4−SECOND TRIAL UNTIL FLAME SENSED.
IS VOLTAGE ABOVE 90 VOLTS?
YES
NO
YES
4−SECOND FLAME STABILIZATION PERIOD.
COMBUSTION AIR INDUCER OFF, IGNITER OFF.
SIGNAL HOLDS UNTIL VOLTAGE RISES ABOVE 95
VOLTS. STATUS ERROR CODE 4 + 8.
NO
FLAME RECTIFICATION CURRENT CHECK
CAN FLAME BE PROVEN WITHIN 4
SECONDS AFTER GAS VALVE OPENS?
(u0.20 microamps)
GAS VALVE OFF. COMBUSTION AIR
INDUCER ON. INDOOR BLOWER OFF.
STATUS LED −− HEARTBEAT.
HAS CONTROL FAILED TO SENSE
FLAME FOR FIVE CONSECUTIVE TRIES
DURING A SINGLE HEAT DEMAND?
NO
YES
WATCHGUARD MODE. GAS VALVE OFF,
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF.
STATUS ERROR CODE 4 + 1.
IS 60−MINUTE RESET PERIOD COMPLETE?
YES
YES
FLAME PRESENT?
YES
CONTINUED ON NEXT PAGE
NO
HAS CONTROL RESET IGNITION SEQUENCE
FOUR (4) TIMES?
WATCHGUARD MODE.
STATUS ERROR CODE 4 + 3.
Page 40
NO
HEATING SEQUENCE OF OPERATION
CONTINUED
THERMOSTAT CALLS FOR HEAT.
STATUS LED −− HEARTBEAT.
SEE BOX A.
FLAME SIGNAL ABOVE
(u1.40 microamps)
NO
LOW FLAME SIGNAL
(Does not affect control operation)
STATUS ERROR CODE 1 + 2.
YES
YES
SINGLE−STAGE THERMOSTAT MODE
(DIP SWITCH SET AT SINGLE")
TWO STAGE THERMOSTAT MODE
(DIP SWITCH SET AT TWO")
YES
YES
START SECOND−STAGE RECOGNITION
ON DELAY (10 OR 15 MINUTES).
STATUS LED −− HEARTBEAT
45−SECOND INDOOR BLOWER ON DELAY BEGINS.
STATUS LED −− HEARTBEAT.
YES
YES
ROLLOUT SWITCHES CLOSED?
PRIMARY & SECONDARY LIMIT SWITCHES
CLOSED?
NO
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER ON.
STATUS ERROR CODE 5 + 1. SEQUENCE HOLDS
UNTIL ROLLOUT SWITCH IS RESET AND MAIN
POWER IS INTERRUPTED OR THERMOSTAT
IS CYCLED OFF/ON FOR 3 SECOND MINIMUM.
YES
YES
FIRST−STAGE (LOW FIRE)
PRESSURE SWITCH CLOSED?
YES
NO
NO
NO
GAS VALVE OFF, COMBUSTION AIR INDUCER OFF,
INDOOR BLOWER ON.
STATUS ERROR CODE 3 + 1.
FIRST−STAGE HEAT DEMAND SATISFIED?
YES
GAS VALVE OFF, COMBUSTION AIR INDUCER
OFF FOLLOWING POST PURGE.
INDOOR BLOWER OFF WITH DELAY
STATUS LED −− PULSE
YES
HAS PRIMARY OR SECONDARY LIMIT
SWITCH CLOSED WITHIN 3 MINUTES?
(Indoor blower on low speed during 3−minute period)
SECOND−STAGE HEAT DEMAND.
SECOND−STAGE HEAT DEMAND REQUIRED?
LIMIT SWITCH WATCHGUARD MODE.
GAS VALVE OFF, COMBUSTION AIR INDUCER OFF,
INDOOR BLOWER OFF WITH DELAY.
YES
STATUS ERROR CODE 4 + 5
IS 60−MINUTE RESET PERIOD COMPLETE?
NO
YES
SECOND STAGE PRESSURE SWITCH CLOSED?
ABNORMAL FLASH CODE.
NOTE − IF SECOND−STAGE PRESSURE SWITCH
WAS ORIGINALLY FOUND CLOSED,
ABNORMAL CODE WILL FLASH.
YES
NO
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF AFTER DELAY.
STATUS ERROR CODE 2 + 3. CONTROL RESTARTS YES
IGNITION SEQUENCE IF PRESSURE SWITCH
CLOSES WITHIN 2−1/2 MINUTES.
SECOND−STAGE PRESSURE SWITCH CLOSED
AT BEGINNING OF HEAT DEMAND?
STATUS ERROR CODE 2 + 6.
SECOND−STAGE 30−SECOND DELAY ON BEGINS.
STATUS LED −− HEARTBEAT.
YES
SECOND−STAGE COMBUSTION AIR INDUCER
ON. SECOND−STAGE GAS VALVE ON. HIGH
HEAT INDOOR BLOWER SPEED ON.
STATUS LED −− HEARTBEAT.
YES
SECOND−STAGE PRESSURE SWITCH CLOSED
IN LESS THAN TEN (10) SECONDS?
STATUS LED −− HEARTBEAT
NO
SECOND STAGE HEAT DEMAND
STATUS LED −− HEARTBEAT.
NO
RETURNS TO FIRST−STAGE HEAT MODE WHICH
CONTINUES UNTIL SECOND−STAGE PRESSURE
SWITCH CAN BE PROVEN or HEAT DEMAND IS
SATISFIED. FIVE (5) MINUTE WAIT PERIOD
INITIATED BEFORE RETRY. WERE 5 ATTEMPTS
MADE FOR SECOND−STAGE HEAT?
YES
CONTINUES FIRST−STAGE HEATING DEMAND.
WILL NOT REATTEMPT SECOND−STAGE
HEATING DEMAND.
STATUS ERROR CODE 2 + 5.
YES
CONTINUED ON NEXT PAGE
Page 41
NO
HEATING SEQUENCE OF OPERATION
CONTINUED
SEE BOX A
NORMAL OPERATION.
SEE BOX B
THERMOSTAT CALLS FOR HEAT.
SECOND−STAGE (HIGH FIRE) HEAT
PRESSURE SWITCH CLOSED?
RETURN TO FIRST−STAGE HEAT MODE.
FIRST−STAGE CONTINUES UNTIL SECOND−
STAGE PRESSURE SWITCH CAN BE PROVEN
or HEAT DEMAND IS SATISFIED. A FIVE (5)
MINUTE WAIT PERIOD IS INITIATED BEFORE
RETRY. WERE 5 ATTEMPTS MADE FOR
SECOND−STAGE HEAT?
NO
SEE BOX C
FIRST−STAGE HEAT DEMAND SATISFIED?
NO
YES
HEAT DEMAND SATISFIED?
STATUS LED −− HEARTBEAT.
YES
YES
TWO STAGE THERMOSTAT MODE?
(DIP SWITCH SET AT TWO")
SINGLE−STAGE THERMOSTAT MODE
(DIP SWITCH SET AT SINGLE")
YES
YES
GAS VALVE OFF, COMBUSTION AIR
INDUCER OFF AFTER 5−SECOND
LOW SPEED POST PURGE PERIOD,
INDOOR BLOWER OFF DELAY
INITIATED ON LOW HEAT SPEED.
STATUS LED −− HEARTBEAT.
YES
YES
FIRST AND SECOND STAGE HEAT
DEMAND SATISFIED SIMULTANEOUSLY.
STATUS LED −− HEARTBEAT.
NO
SECOND STAGE HEAT
DEMAND SASTISFIED?
STATUS LED −− HEARTBEAT.
YES
GAS VALVE, COMBUSTION AIR INDUCER
AND INDOOR BLOWER RETURN TO FIRST−
STAGE OPERATION.
STATUS LED −− HEARTBEAT.
FIRST STAGE HEAT DEMAND SATISFIED?
YES
GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF AFTER 5−SECOND LOW SPEED POST−
PURGE PERIOD. INDOOR BLOWER OFF.
DELAY INITIATED ON LOW HEAT SPEED.
STATUS LED −− PULSE.
DEMAND FOR HEAT SATISFIED.
POWER ON STAND BY.
STATUS LED −− PULSE.
Page 42
COOLING SEQUENCE OF OPERATION
POWER ON
YES
IS POLARITY REVERSED?
SIGNAL POLARITY REVERSED.
CONTROL WILL CONTINUE TO CALL FOR COOLING
IN THIS CONDITION.
STATUS ERROR CODE 5 + 4.
NO
SIGNAL IMPROPER GROUND AT LED.
CONTROL WILL CONTINUE TO CALL FOR COOLING
IN THIS CONDITION.
STATUS ERROR CODE 5 + 3.
NO
IS THERE
PROPER GROUND?
YES
THERMOSTAT CALLS FOR FIRST−STAGE COOL.
COMPRESSOR AND CONDENSER FAN
ENERGIZED.
INDOOR BLOWER ENERGIZED ON FIRST STAGE
COOL SPEED AFTER 2 SECOND DELAY.
FIRST−STAGE DEMAND FOR COOL SATISFIED?
YES
NO
THERMOSTAT CALLS FOR SECOND−STAGE COOL.
INDOOR BLOWER RAMPS UP TO SECOND−STAGE COOL SPEED.
SECOND−STAGE DEMAND FOR COOL SATISFIED?
YES
UNIT RETURNS TO FIRST STAGE COOL
Page 43
COMPRESSOR AND CONDENSER FAN DE−ENERGIZED.
INDOOR BLOWER DE−ENEGIZED.
CONTINUOUS LOW SPEED FAN SEQUENCE OF OPERATION
MANUAL FAN SELECTION MADE AT THERMOSTAT.
AFTER 2 SECOND DELAY, INDOOR BLOWER IS
ENERGIZED ON CONTINUOUS FAN SPEED.
YES
YES
THERMOSTAT CALLS FOR FIRST STAGE COOL.
YES
YES
INDOOR BLOWER RAMPS TO FIRST STAGE
COOLING SPEED AFTER A 2−SECOND DELAY.
YES
THERMOSTAT CALLS FOR FIRST−STAGE HEAT.
AFTER 45−SECOND DELAY, INDOOR BLOWER
SWITCHES TO LOW HEAT SPEED.
FIRST−STAGE COOL DEMAND SATISFIED?
FIRST−STAGE HEAT DEMAND SATISFIED.
NO
NO
SECOND STAGE COOL DEMAND
THERMOSTAT CALLS FOR SECOND−STAGE HEAT.
YES
INDOOR BLOWER RAMPS TO SECOND
STAGE COOL SPEED
INDOOR BLOWER SWITCHES TO HIGH HEAT SPEED
AFTER 30−SECOND RECOGNITION PERIOD.
YES
SECOND STAGE COOL DEMAND SATISFIED?
SECOND−STAGE HEAT DEMAND SATISFIED.
YES
YES
INDOOR BLOWER RAMPS DOWN TO FIRST STAGE
COOL SPEED.
Page 44
INDOOR BLOWER RAMPS DOWN TO LOW
HEAT SPEED.
YES
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