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Operation
49RT-SVX20A-E4
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
five minute delay before the new
call will initiate.
Thermostat signals are as follows:
R 24VAC power to thermostat
Y1 Call for compressor 1 or first
stage cooling
Y2 Call for compressor 2 or 2nd
stage cooling
G Call for supply fan
W1 Call for heat 1
W2 Call for heat 2
Heat pump only:
X2 Call for emergency heat
O Switchover valve On = cooling,
Off = heating
T Bias for heat anticipation for those
mechanical thermostats that use
this function
Table 44
Table 45
Conventional thermostat Heat pump
Input / connection Function when energized
Cooling mode
G (fan) Fan runs continuously except during unoccupied mode (see next page)
O (reversing valve during cooling) Reversing valve in cool mode
Y1 + O (first cooling stage) Compressor #1 runs or economizer operates
Y1 + Y2 + O (2nd cooling stage) Compressor #2 also runs, or #1 compressor runs while economizing
Heating mode
G (fan) Fan runs continuously except during unoccupied mode (see next page)
Y1 (both compressors 1st heating stage) Both compressors run
Y2 (during heating nothing happens) No change
W2 (electric heat 2nd stage) 2nd stage (electric) heat
X2 (electric heat only) Electric heat only - no compressors
T (provides heat anticipation signal for those mechanical
thermostats that use this feature.
If the thermostat used does not have a "T" terminal, disregard
this terminal.)
Conventional thermostat Gas / Electric, Electric Heat
Input / connection Function when energized
G (fan) Fan runs continuously except during unoccupied mode (see next page)
Y1 (compressor 1 or economizer) Compressor #1 runs or economizer operates
Y2 (compressor 2 or compressor 1 while economizing) Compressor #2 also runs, or #1 compressor runs while economizing
W1 (gas / electric heat first stage) 1st stage heat
W2 (gas / electric heat 2nd stage) 2nd stage heat (if available)
Conventional thermostat signals
represent direct calls for unit
functions. In their simplest
applications, thermostat contacts
directly control contactors or other
load switching devices. 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.