Installation Instructions
MAC/MGH Furnace
Installation Instructions
and
Replacement Fan/Limit – Part No. 902909
These instructions are primarily intended to assist qualified individuals experienced in the proper installation of this
appliance. Some local codes require licensed installation/service personnel for this type of equipment. Read all
instructions carefully before starting the installation. NOTE: CONTROL COMES PRE-WIRED FOR MAC FURNACE
INSTALLATION. MAKE APPROPRIATE WIRE CHANGES FOR MGH FURNACES (SEE FIGURE 2).
INSTALLATION SEQUENCE
MAC 1175 FURNACE
1. Remove the cover from the control box.
7. Run the wires attached to the timer through the
bushing at the bottom of the control box and install the
bushing.
2. Attach the timer to the outside bottom edge of the
control box cover.
8. Connect the wires per the wiring diagram. (See
Figure 1)
3. Remove the bushing from the bottom of the control
box.
9. Attach the control box cover.
4. Remove the fan/limit combination control.
10. DELAY ON MAKE dial should be set for 60 seconds.
5. Install the limit into the opening from the old fan/limit
combination control.
11. DELAY ON BREAK dial should be set for 120
seconds.
6. Remove the wires attached to the old fan/limit control.
Air Circulator
Receptacle
Summer Air Circulator
Receptacle
Unit Switch
MAC 1175
BLACK
WHITE
BLACK
BLACK
BLACK
Terminal Board
WHITE
YELLOW
BLACK
Equipment
Ground
24V Leads to
Thermostat
YELLOW
YELLOW
RED
RED
WHITE
WHITE
Gas Valve
RED
120V
Transformer
24V
+
WHITE
-
DELAY
ON
BREAK
G
Timer
Limit
Switch
Figure 1. MAC 1175 Wiring Diagram
DELAY
ON
MAKE
COM
C
R
L
NO
NC
INSTALLATION SEQUENCE
MGH FURNACE
Models MG(-) -075 and -100 Gas Atmospheric Furnaces
Control Panel Cover
Green
Ground
Screw
WHITE
BLACK
24V Leads to
Thermostat
3
BLACK
RED
BLOWER
RECEPTACLE
WHITE
BLUE
YELLOW
BROWN
Limit
3 Position
Switch
BLACK
BLUE
BLACK
BLACK
1
WHITE
BLACK
Auxiliary
Limit Control
At Bottom Of
Heat Exchanger
2
3
2
FAN OFF
YELLOW
1
ON
BLUE
BLACK
BLACK
Gas Valve
Control Panel Cover
YELLOW
Transformer
25V
YELLOW
RED
DELAY
G
ON
BREAK
C
DELAY
NO
ON COM
MAKE
R
L
BLUE
RED
RED
RED
BLUE
RED
120V
NC
BLUE
BLUE
Figure 2. MGH Furnace Wiring Diagram
INSTALLER:
PLEASE LEAVE THESE
INSTALLATION INSTRUCTIONS
WITH THE HOMEOWNER.
¢708052§¤
St. Louis, MO
708052
7080520 (Replaces 707390A)
Specifications and illustrations subject to change
without notice and without incurring obligations.
Printed in U.S.A. (12/00)
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