40 | Sequence of Operation SM Series Heat Pump
SM Series Heat Pump6 720 220 406 (2013/1) Subject to change without prior notice
SEQUENCE OF OPERATION
Cooling Mode
Energizing the “O” terminal energizes the unit
reversing valve in the cooling mode. The fan motor
starts when the “G” terminal is energized. Note
that the fan motor will take 30 seconds to ramp up
to operating speed and will run at fan only rated air
fl ow as long as there is no call for compressor or
heater operation.
When the thermostat calls for first stage cooling
(Y1) the loop pump or solenoid valve if present is
energized and the first stage of compressor
capacity starts. The fan ramps up to first stage
cooling air flow in 30 seconds.
When the thermostat calls for second stage
cooling (Y2) the second stage (or full compressor
capacity) is initiated. The fan ramps up to full
cooling air flow.
Once the thermostat is satisfied, the compressor
shuts down accordingly and the fan ramps down to
either fan only mode or off over a span of 30
seconds.
Heating Mode
The first two stages of heating (Y1 & Y2) operate in
the same manner as cooling, but with the reversing
valve de-energized. On a call for auxiliary heat
(W1), the fan ramps up to auxiliary heat air fl ow
immediately and the electric heater package is
energized along with the compressor. As the
thermostat is satisfied, the heaters will shut off as
soon as W1 is de-energized, and the compressors
will remain on until the thermostat stages are
satisfied. Note that if the unit compressor lock out
for any reason at this time, the electric heaters will
continue to function normally. Once the
thermostat is satisfied, the compressor shuts
down and the fan ramps down either fan only
mode or off over a span of 30 seconds. If
thermostat has two different output points one for
Auxiliary heat and a different one for Emergency
heat the two outputs must be terminated on W1
units equipped with one stage of Electric heat.
(Figure #104)
Note that a fault condition initiating a lockout will
de-energize the compressor irrespective of
which stage is engaged.
When using a 2-cool, 3-heat thermostat W1 and
W2/EM must be connected together via a
jumper.
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