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9.0 SEQUENCE OF OPERATION
9.1 Cooling (cooling only or heat pump)
• When the thermostat "calls for cooling," the circuit between R, G and Y is completed,
causing the blower to energize. This circuit also closes the contactor (CC) in the out-
door unit starting the compressor (COMP) and outdoor fan motor (OFM).
9.2 Heating (electric heat only)
• When the thermostat "calls for heat," the circuit between R and W
the heater sequencer (HR
elements (HE) and the indoor blower motor (IBM) will come on. Units with a second
heater sequencer (HR
) can be connected with the first sequencer (HR
2
thermostat sub-base or connected to a second stage W
W
on the furnace board MUST be connected for heating blower operation.
1
9.3 Heating (heat pump)
• When the thermostat "calls for heat," the circuits between R and G are completed.
Circuit R and B energizes the reversing valve (RV) switching it to the heating position
(remains energized as long as system switch is in "heat" position). Circuit R and Y
energizes the contactor (CC) starting the outdoor fan motor (OFM), compressor
(COMP), and the indoor blower motor (IBM).
• If the room temperature should continue to fall, circuit R and W
second-stage heat room thermostat. Circuit R-W
The completed circuit will energize supplemental electric heat. Units with a second
heater sequencer (HR
) can be connected with first sequencer (HR
2
stat or connected to a third heating stage W
the thermostat indicates when supplemental heat is being energized.
9.4 WATT RESTRICTOR
(Heating - Heat Pump)
• Heat pump air handlers with supplemental electric heat above a specific kW depen-
dent on unit size and total heater kW are equipped with a patented watt restrictor.
Models so equipped are Cabinet Model Size -14 with more than 6 kW Cabinet Model
Size -17, -21 and -24 with more than 11 kW Watt restrictor (WR) may directly control
a heater element in the heater circuit or may be in the control circuit controlling heater
sequencer (HR
) indirectly controlling two or three heater elements (HE) (see unit
2
wiring diagram).
• The watt restrictor (WR) will restrict the amount of supplemental electric heat that can
be energized dependent on the heat output of the heat pump (temperature of the air
leaving the indoor heat pump coil).
Since the heat output of the heat pump is dependent upon the outdoor air temperature,
this control performs the same function as a field installed outdoor thermostat,.
An additional benefit of the watt restrictor is that it can sense a degradation in heat pump
performance due to causes other than outdoor temperature and react accordingly to
bring on more supplemental electric heat.
9.5 DEFROST SEQUENCE
• For sequence of operation for defrost controls, see outdoor heat pump installation
instructions.
• Supplemental heat during defrost can be provided by connecting the purple (PU) pig-
tail in the outdoor unit to P on the indoor unit control board. This will complete the cir-
cuit between R and W through a set of contacts in the defrost relay (DR) when the
outdoor heat pump is in defrost. This circuit, if connected, will temper air being dis-
charged from the indoor unit during defrost.
• Defrost heat control (DHC) is wired in series in the circuit described above on units
where the supplemental heat is more than would be required to offset the defrost
cooling capacity. Defrost heat control (DHC) is provided on the same models
described above having watt restrictors.
• When the outdoor unit goes into defrost, the circuit between R and W is completed
through a set of contacts on the defrost relay (DR) in series with the contacts on the
defrost heat control (DHC). Purple (PU) pigtails on the indoor unit and outdoor units
must be connected to make circuit. During defrost, the defrost heat control (DHC)
senses the air temperature leaving the indoor unit and cycles the supplemental elec-
tric heat to maintain comfort (75° to 85°) air temperature and prevent objectable cold
air during defrost. This limits the electric heat output to the minimum required, to con-
serve energy and prevent the thermostat from being satisfied with electric heat and
preventing completion of the defrost cycle.
) is energized. A time delay will follow then: The heating
1
energizes a heat sequencer (HR
2
on the thermostat sub-base. A light on
3
is completed, and
1
) to W on the
1
on the sub-base.
2
is completed by the
2
).
1
) to W
on thermo-
1
2
25
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