BAS-SVU054A-EN
17
Thermostats and Zone Sensors
Thermostats
Customers occasionally require operation with a conventional thermostat rather than a zone
sensor. Non-Trane building controllers typically provide an interface to HVAC equipment based
on a conventional thermostat interface. Units applied with this type of controller need to accept
conventional thermostat inputs. Conventional thermostat signals represent direct requests for
unit functions. This function provides inputs for the thermostat signals and processing to
enhance reliability and performance. Compressor protection and reliability enhancement
functions (HPC, LPC, minimum On/Off timers, etc.) all operate the same whether applied with
zone sensors or a conventional thermostat. Logic is also provided to cause appropriate unit
functions when inappropriate thermostat signals are provided. Simultaneous calls for heating
and cooling will be ignored, and the fan will be turned on with a call for heating or cooling even if
the fan request is not detected. If the thermostat is immediately changed from a heating to a
cooling call, or vice versa, there will be a delay before the new mode will initiate.
Table 7. Thermostat signals
Thermostat Operation Signal
J21 terminal
(1) R 24VAC power to thermostat
(2) Y1 Call for stage 1 of cooling
(6) Y2 Call for stage 2 of cooling
(4) G Call for supply fan
(3) W1 Call for stage 1 of heating
(5) W2 Call for stage 2 of heating
Heat pump only
(7) X2 Call for emergency heat
(3) O Switchover valve On = cooling, Off = heating
Conventional thermostat – gas/
electric, electric heat
G (fan) Fan runs continuously
Y1 (first stage of cooling) Compressor 1 runs
Y2 + Y2 (second stage of cooling) Compressor 1 and Compressor 2 runs
W1 (first stage of heating) Electric first stage operates
W2 (second stage of heating) Electric second stage operates
Conventional thermostat – heat
pump
G (fan) Fan runs continuously
O (reversing valve during cooling) Reversing valve in cool mode
Y1 + O (first stage cooling) Compressor 1 runs
Y1 + Y2 + O (second stage of cooling) Compressor 1 and Compressor 2 will run
Zone Sensors
A 10k ohm resistance type 2 thermistor can be wired to terminals J19-1 and J19-2 as an input for
space temperature.
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In some applications, 1 zone sensor does not give a good representation of zone temperature.
The internal thermistors, 10K ohm resistance @ 25C/77F, can be wired as shown below in order
to provide an average input to the J19-1 and J19-2 terminals
Figure 6. Zone sensors
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