IN ALL THREE RESET METHODS DESCRIBED ABOVE,
A FIVE MINUTE TIME DELAY WILL TAKE PLACE AFTER
THE RESET BEFORE THE UNIT WILL RESTART.
8. Supplemental electric heat (if installed) will be controlled by
second stage TH2 of the thermostat. The supplemental
electric heat circuit is controlled through low voltage termi-
nals W, 60 and 66. The standby portion of electric heat
(controlled through low voltage terminal 53) cannot operate
because relay 4R is energized, opening the circuit to termi-
nal 53, whenever the compressor is operating.
9. When second stage heating TH2 is satisfied, the supple-
mental heaters will be de-energized.
DEFROST CYCLE
When condensate freezes on the outdoor coil during heating
operation, it must be defrosted before it blocks the flow of air
across the coil.
1. A defrost cycle will be initiated by the defrost control board's
timed defrost feature.
2. When the defrost cycle is initiated, the unit operates as fol-
lows:
a. The reversing valve solenoid is energized through the
defrost control board causing the unit to switch to the
cooling cycle.
b. Defrost control board de-energizes 2M contactor, caus-
ing the outdoor section fan(s) to shut down.
c. Supplemental electric heat (if installed) will be ener-
gized through defrost control board. Only that portion of
electric heat controlled through low voltage control ter-
minal 66 will be energized by the defrost cycle. The op-
eration of supplemental electric heat during unit defrost
will prevent cold drafts in the conditioned space.
3. The defrost cycle will be terminated when:
a. the liquid temperature exceeds 55
°
F, or
b. 10 minutes have passed since defrost initiation.
The 10 minute cycle time (independent of liquid line tem-
perature) is controlled by the defrost control board.
4. At defrost termination, the unit returns to the normal heat-
ing operation.
OPERATION BELOW 0
°
F OUTDOOR
TEMPERATURE
1. At 0
°
F outdoor temperature, the low temperature compres-
sor cutoff thermostat 1TH contacts 1 and 3 will open, de-
energizing contactor 1M which shuts down the compres-
sor. Contacts 1 and 2 of thermostat 1TH are closed when
contacts 1 and 3 are open. This feature allows the standby
electric heat (if installed) to operate under control of first
stage heating TH1 of the room thermostat whenever the
compressor is shut-down by the 1TH control. The supple-
mental electric heat will continue to be controlled by the
second stage TH2 of the room thermostat same as de-
scribed under Item 8 of HEATING OPERATION.
2. The indoor section blower operation will be controlled by
the first stage heating TH1 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. Compressor will not operate because the Y circuit of the
room thermostat cannot be energized.
3. Supplemental and 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.
035-15410-002-B-0404
14
Unitary Products Group
