SEQUENCE OF OPERATION
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 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. 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 option out-
door thermostat 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 position:
1. Emergency light is energized.
2. Compressor circuit is locked out.
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.
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, even though the limits close and
will start up only when the lockout is reset. Since there is no “X”
output on this control, no malfunction indication light will illumi-
nate on the thermostat. 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 trans-
former for at least two seconds. Please note that thermostats
with anti-short cycle timers will only be able to reset by discon-
necting the power to the transformer for at least two seconds.
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.
The electronic timer and the defrost cycle will start only when
the contactor is energized and the defrost thermostat is closed.
The defrost thermostat is closed when the liquid temperature
falls below approximately 31
°
F.
The defrost mode is identical to the cooling mode except that
the outdoor fan motor stops and the first stage of heat (5KW if
electric heat) is turned on through W1 / 66 to continue
warming the conditioned space.
The defrost cycle will be terminated when the defrost thermo-
stat is opened at 60
°
F or 10 minutes of compressor accumu-
lated run time, whichever comes first. Note: The defrost
thermostat delay will make the coil temperature about 75 - 80
°
F.
Please note that the timer will stop the circuit when R to Y is
disconnected.
TEST PIN:
The “TEST” terminals are designed for defrost test. When the
“TEST” terminals are shorted together, the control will allow the
unit to go into a defrost cycle if the compressor is operating.
When the short is removed, the heat pump will remain in defrost
until the defrost thermostat is open or 10 minutes expires. If the
thermostat is open when the short is removed, the heat pump
will exit defrost.
FIGURE 12 - TIME / TEMPERATURE DEFROST BOARD
TEST
W
W1/66
Y
O
90
C
RUN TIME
90
60
30
60
30
SEL MIN
U1
COND FAN
K2
K3
R2
K1
HIGH VOLTAGE
PRESSURE
SWITCH
REVERSING
VALVE
DEFROST
STAT
C
C
COMPRESSOR
RELAY
C
R
R
TIME
SELECTION
TAP
DEFROST
TEST
PIN
M
THERMOSTAT
515.26-N5Y
Unitary Products Group
11
