15
W
R
G
C
Y
W
R
G
Y
Standard Furnace Interlock Wiring
THERMOSTAT
TERMINALS
FURNACE
24-VOLT
TERMINAL BLOCK
FOUR
WIRE
TWO WIRE
heating only
TWO
WIRE
COOLING SYSTEM
W
R
G
C
Y
W
R
G
Y
Alternate Furnace Interlock Wiring
THERMOSTAT
TERMINALS
FURNACE
24-VOLT
TERMINAL BLOCK
FOUR
WIRE
TWO WIRE
heating only
TWO
WIRE
COOLING SYSTEM
WIRE JOINT
WIRING DIAGRAM
(CONT'D)
WIRING DIAGRAM TO
FURNACE
FOR A FURNACE
CONNECTION TO
A COOLING SYSTEM:
On some newer furnaces and
older thermostats, energizing the
R and G terminal at the furnace
has the effect of energizing the
Y at the thermostat and thereby
turning on the cooling system. If
you identify this type of thermo-
stat, you must use the “Alternate
Furnace Interlock Wiring”
Standard Accessory Control Contact
Alternative Accessory Control Contact
AS PER BUILDING CODES AND INSTALLATION REqUIREMENTS FOR COMBUSTION APPLIANCES: AIR RETURN
DUCTS, OR OPENINGS FOR AIR RETURN, SHOULD NOT BE PLACED IN ENCLOSED SPACES CONTAINING
COMBUSTION APPLIANCES THAT ARE SUBJECT TO SPILLAGE