035-15713-003 REV. A (0500)
Unitary Products Group
13
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
(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). Cir-
cuit 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 supplement 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
temperature. The outdoor thermostat is a requirement for
manufactured housing installations. If gas/propane furnace is
used as the supplement heat, add-on control kit 3024-7481
must be used. See the add-on control installation instruction
for the system operation.
EMERGENCY HEAT
When the switch on the thermostat is placed in emergency
heat position:
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 con-
tactor, stopping the compressor in response to the high pres-
sure (#400) limit switch opening for more than one second.
the compressor will remain off until the high pressure switch
recloses. 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 thermo-
stat's system switch to "OFF" then, back to the selected
mode OR disconnect 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 14.
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 tem-
perature 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 warm-
ing the conditioned space.
The defrost cycle will be terminated when the defrost thermo-
stat is opened at 55° F or 10 minutes of compressor accumu-
lated run time, whichever comes first.
NOTE:
The defrost thermostat delay will make the coil tem-
perature about 75-80° F. Please note that the timer
will stop the circuit when R to Y is disconnected.
TEST PIN ON TIME/TEMPERATURE DEFROST:
The “test” terminals are designed for two uses:
1.
Anti-Short Cycle By-Pass -
To by-pass the anti-short
cycle feature in the control, jumper the two "test" termi-
nals for at least 2 seconds. If there is a "Y" signal to the
control, jumpering the test terminal will allow the control
to pull in the unit contactor immediately.
NOTE:
Do not hold the jumper on the test terminal for more
than 5 seconds as the control will go into the defrost
mode.
2.
Forced Defrost -
To force the unit into the defrost mode
(24V to Reversing Valve and no fan operation) while the
unit is operating, jumper the test terminals for 2 seconds
if the unit was running (if the unit was not running and
step 1 above was used to start the unit, then the "test"
terminals must be held for at least 10 seconds). When
the short is removed, the heat pump will remain in
defrost until the defrost thermostat opens or 10 minutes
expires. If the thermostat is open when the short is
removed, the heat pump will exit defrost immediately.
14 SEER WITH DEMAND DEFROST
SAFETY LOCKOUT MODE:
The lock out control opens the circuits to the compressor con-
tactor, stopping the compressor in response to the high pres-
sure (#400) limit switch or the high discharge temperature
switch. The control goes 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 OR disconnect the power to
the transformer for at least 2 seconds. Please note that ther-
mostats with anti-short cycle timers will only be able to reset
by disconnecting the power to the transformer for at least 2
seconds.
