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OPERATION BELOW 0° F OUTDOOR TEMPERA
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TURE
1.
At 0°F outdoortemperature, the low temperaturecompres
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sor cutoff thermostat TH1 and TH3 contacts 1 and 3 will
open, de-energizing contactor 1M and 3M which shuts
down the compressor. Contacts 1 and 2 of thermostat TH1
and TH3 are closed when contacts 1 and 3 are open. This
featureallows thestandbyelectricheat(if installed)to oper
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ateundercontrol offirststageheatingTH1 oftheroomther
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mostat whenever the compressor is shut-down by the 1TH
control. The standby electric heat will continue to be con
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trolled by the second stage TH2 of the room thermostat
same as described under Item 8 of HEATING OPERA
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TION.
2. The indoor section blower operation will be controlled by
the first stage heatingTH1 of the room thermostat if the fan
switch is in the “AUTO” position.
EMERGENCY HEAT OPERATION
When the system switch on the room thermostat is placed in
the EMERGENCY HEAT position, operation is as follows:
1. The emergency heat light on the room thermostat will be
energized.
2. Compressors will not operate because the Y circuit of the
room thermostat cannot be energized.
3. Standby electric heat (if installed) will be controlled by first
stage heating TH1 of room thermostat.
4. Indoor section blower will also be controlled by first stage
heating TH1 if fan switch is in the “AUTO” position.
Unitary Products Group 13
035-16192-001-A-1001