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Sequence of Operation
Cooling (cooling only or heat pump)
Single Stage Cooling
For single stage cooling, Y1 and Y2 need to be jumpered.
When the thermostat calls for cooling, the circuit between R
and G is completed, and the blower relay is energized. The
Normally Open contacts close, causing the indoor blower
motor to operate. The circuit between R and Y is also
completed; this circuit closes the contactor in the outdoor
unit starting the compressor and outdoor fan motor. Circuit
R and O energizes the reversing valve switching it to the
cooling position. (The reversing valve remains energized
as long as selector switch is in the COOL position.)
Two Stage Cooling
On a call for 1st stage cooling, the thermostat closes R
to Y. In 1st stage cooling, the blower runs at 70% of the
the thermostat closes R to Y2. In 2nd stage cooling, the
Heating (electric heat only)
When the thermostat calls for heat, the circuit between R
and W is completed, and the heater sequencer is energized.
A time delay follows before the heating elements and the
indoor blower motor come on. Units with a second heat
W on the thermostat sub-base or connected to a second
stage on the sub-base.
Heating (heat pump)
When the thermostat calls for heat, the circuits between R
and Y and R and G are completed. Circuit R-Y energizes
the contactor starting the outdoor fan motor and the
compressor. Circuit R and G energizes the blower relay
starting the indoor blower motor.
If the room temperature should continue to fall, the
circuit between R and W1 is completed by the second
stage heat room thermostat. Circuit R-W1 energizes
a heat sequencer. The completed circuit will energize
supplemental electric heat. Units with a second heater
W1 on the thermostat or connected to a second heating
stage W2 on the thermostat sub-base.
Emergency Heat (heating heat pump)
If selector switch on thermostat is set to the emergency
heat position, the heat pump will be locked out of the
heating circuit, and all heating will be electric heat. A jumper
should be placed between W2 and E on the thermostat
sub-base so that the electric heat control will transfer to the
blower to cycle on and off with the electric heat when the
fan switch is in the AUTO position.
Page 8
mrcool.com
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