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HVAC system testing
If you have difficulty with the HVAC system operation, you can do the following test to verify the HVAC
system is operational.
Thermostats, like the SmartCommand thermostat, are just switches to the HVAC system as shown in the
Figure 20. This is a simplified example of a thermostat and a standard HVAC wiring diagram. You can test the
HVAC system operation by duplicating the thermostat switch operation by shorting across the thermostat
terminals on the HVAC system.
Figure 20. HVAC system wiring example
Note: The HVAC system and thermostat connection voltage is 24 VAC. This is a safe voltage to work with, but be careful to
avoid shorting the 24 VAC common (C) and 24 VAC return (R) terminals. This may blow a fuse in the HVAC system.
Typical thermostat
HVAC system (standard gas/AC)
Fan
Heat
Comp
Thermostat
connection
C 24 VAC common
R 24 VAC hot
G Fan
W Heat
Y Comp
24 VAC
Fan relay
Gas valve
Comp relay