COOLING
On call for cooling, the thermostat makes 24V circuits: R to O,
R to Y, and R to G. Circuit R to O energizes the reversing valve,
switching it to cooling position. Circuit R to Y energizes the
contactor, starting outdoor fan motor and compressor (after the
anti-short cycle period). Circuit R to G energizes the indoor
unit blower relay, starting the indoor blower motor.
HEATING
On call for heating, thermostat makes circuits R to Y and R to
G. Circuit R to Y energizes contactor, starting outdoor fan motor
and compressor (after the anti-short cycle period). Circuit R to
G energizes the indoor blower relay, starting the blower motor.
Should the temperature continue to fall, R to W is made through
the second stage of the thermostat. Circuit R to W energizes
the supplemental electric heat. The field-installed outdoor
thermostat option can be used to turn on only the first stage of
electric heat if the temperature is above the setting tempera-
ture. If gas/propane furnace is used as the supplemental heat,
add-on control kit (2AC02700701) must be used. See the
add-on control installation instruction for the system operation.
EMERGENCY HEAT
When switch on thermostat is placed in emergency heat posi-
tion:
1. Emergency light is energized.
2. Compressor circuit is locked out. (No "R" to "Y")
3. Supplemental and standby heaters (if installed) will be
controlled by first stage of heating thermostat.
4. Indoor blower will operate on demand for heat and cycle off
with the last heater element when in “AUTO” position.
10 & 12 SEER WITH TIME / TEMP. DEFROST
SAFETY LOCKOUT MODE:
The lock out control opens the circuits to the compressor
contactor, stopping the compressor in response to (400 #) High
Pressure limit switch opening for more than one second. The
compressor will remain off until the high pressure switch re-
closes. During the period the switch is open, the control will
provide a pulsed output at the "X" terminal to indicate the
lock-out condition. After the high pressure switch recloses, the
compressor can restart after a 5 minute anti-short cycle period.
If the unit experiences a second high pressure switch opening
within a six hour period, the control will go into a lockout
condition and will not allow the compressor to restart unless
reset. To reset the lockout, turn the indoor thermostat’s system
switch to “OFF” then, back to the selected mode within 5 second
OR disconnect the power to the transformer for at least two
seconds. Please note that thermostats with anti-short cycle
timers will only be able to reset by disconnecting the power to
the transformer for at least two seconds.
TIME / TEMPERATURE DEFROST:
The defrost control is a time/temp control which includes a
field-selectable (white tap located at board edge) time period
between defrost cycle (30, 60, and 90 minutes). Factory set at
60 minutes. See Figure 10.
Pressure
Switch
Reversing
Valve
Defrost
Thermostat
Compressor
Relay
Time Selection Tap
Test Pin
FIGURE 10 - TIME/TEMPERATURE DEFROST (10 &
12 SEER Single Phase) and (10 SEER, Three Phase)
Ambient
Sensor
Reversing
Valve
Defrost Coil
Sensor
Compressor
Relay
High Pressure &
High Temp. Switch
Test
Pin
B
Y
O
66
R
W
X
BLK
BLK BLU BLU YEL YEL
B
B
M
P
Y
O
Defrost
Speedup
FIGURE 11 - DEMAND DEFROST (14 SEER)
SEQUENCE OF OPERATION
515.16-N3Y
Unitary Products Group
9
