System information

DCN: 141-01070-03 TR40 Thermostat Manual 30
HVAC SYSTEM QUICK TEST
The TR40 Control Unit connects to the HVAC system at the normal thermostat connections on the HVAC
unit. Standard thermostat control of HVAC systems consist of contact closures in the thermostat. You can
verify that your HVAC system is working correctly by duplicating these contact closures by shorting across
the proper terminals on the HVAC system. Refer to the following HVAC system example.
HVAC SYSTEM EXAMPLE
Since the thermostat interface is simple switch closures, if you have difficulty with the Control Unit and HVAC
interface you can always verify HVAC system operation by shorting across the HVAC system terminals as
follows:
For Standard HVAC systems:
FAN operation: Short across R and G (Fan) terminals.
HEAT operation: Short across R and W (Heat) terminals (Fan is not usually necessary for gas furnaces).
COOL operation: Short across R and Y (Compressor) and G (Fan) terminals.
For Heat Pump systems (with Change Over for cooling):
FAN operation: Short across R and G terminals.
HEAT Stage 1 operation: Short across R and Y (Compressor) and G (Fan) terminals.
HEAT Stage 2 operation: Short across R and W (Heat Strips) and G (Fan) terminals.
COOL operation: Short across R and Y (Compressor) and O (Change Over) and G (Fan) terminals.
If the Control Unit output LEDs are ON and you suspect you are not getting an output from the relays,
perform the above shorting test to verify that the HVAC system is working OK. If the HVAC system responds
correctly to the shorted terminals, then the output relay is suspect.
B 24VAC COMMON
R 24VAC HOT
G FAN
W HEAT
Y COMP
HVAC SYSTEM
STANDARD GAS/AC
FAN
RELAY
GAS
VALVE
COMP
RELAY
24VAC
This is a simplified diagram of an HVAC System and
Thermostat. The Thermostat operates like switches to
control the HVAC Heat, Cool and Fan functions.
FAN
HEAT
COMP
OUTDOOR
CONDENSING
UNIT
FURNACE AND BLOWER UNIT
THERMOSTAT