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 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 / TEMP. 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" terminals
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 9 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
contactor, stopping the compressor in response to the high
pressure (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 modeOR 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.
DEMAND DEFROST:
The defrost control is a demand defrost control. See Figure 11.
Due to the arrangement of the refrigerant circuit within the
outdoor coil of these units, frost may accumulate unevenly in
different sections of the coil. However, a normal defrost may
occur even though the coil is not completely covered with frost.
The defrost cycle will start only under the following conditions:
1.
Contactor is energized.
2.
A minimum of 39 minutes have elapsed since the last
defrost.
3.
The liquid temperature measured by defrost coil sensor
must be less than 40
°
F.
FLOW
RATER
(cooling)
INDOOR COIL
COMPRESSOR
4-WAY
REVERSING
VALVE*
SUCTION
ACCUMULATOR
OUTDOOR
COIL
COOLING CYCLE FLOW
HEATING CYCLE FLOW
* SHOWN IN COOLING POSITION
FIELD CONNECTED LINE
FIELD CONNECTED LINE
LIQUID
SENSOR
FLOW RATER (heating)
FILTER DRYER
(solid core).
FIGURE 12 - FLOW DIAGRAM - 018 thru 048
—(10 & 12 SEER Single Phase) & (036 - 060, 10 SEER, Three Phase)
515.16-N3Y
10
Unitary Products Group
