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INSTALLATION INSTRUCTIONS
DEFROST SYSTEM
A. DEFROST THERMOSTAT
The defrost thermostat is factory installed on a short tube
stub extending from the coil end plate. Refer to Figure 11
and confirm that the thermostat is securely fastened in
place on the tube stub.
Figure 11
Defrost Thermostat
FEEDER TUBE
B. DEFROST CONTROL BOARD
The defrost board is a time/temperature control which
includes a field−selectable time period between defrost
cycles of 30, 60, or 90 minutes (quick−connects located
at board edge, factory set at 90 minutes).
Defrost mode is identical to cooling mode except that
outdoor−fan motor stops and second−stage heat is
turned on to continue warming conditioned space.
Initially, the defrost cycle timer starts when the contactor
is energized and a 24 VAC signal is present on the T1
terminal. Then the defrost cycle begins when the defrost
thermostat is closed and the cycle timer times out (30, 60,
90 or minutes).
To initiate a forced defrost cycle, the defrost thermostat
must be closed. This can be accomplished as follows:
1. Turn off power to outdoor unit.
2. Disconnect outdoor fan−motor lead from OF2 on
control board (refer to Figure 12). Tape lead to
prevent grounding.
3. Restart unit in heating mode, allowing frost to
accumulate on outdoor coil.
4. After a few minutes in heating mode, liquid line
temperature should drop below closing point of
defrost thermostat, approximately 32° F (0° C).
5. Short between speed−up terminals with a
flat−bladed screwdriver (refer to Figure 12). This
reduces the timing sequence to 7, 14, or 21
seconds (30, 60, or 90 minute defrost selection,
respectively).
START−UP PROCEDURE
1. Set indoor thermostat selector switch to OFF.
2. Turn ON all electrical disconnect devices.
3. If unit has a crankcase heater, energize the heater
and wait 24 hours before proceeding.
428 01 5102 00
6. When you hear reversing valve change position,
NOTE: Length of defrost cycle is dependent upon length
of time it takes to remove screwdriver from test pins after
reversing valve has shifted.
7. Unit will remain in defrost for remainder of
TUBE STUB
8. Turn off power to outdoor unit and reconnect
COIL
Figure 12
DEFROST
THERMOSTAT
4. Set indoor thermostat at desired temperature. Be
5. Set indoor thermostat selector switch to COOL or
R−410A Split System Heat Pump
remove
screwdriver
immediately;
control will terminate normal 10−minute defrost
cycle in approximately 2 seconds.
defrost−cycle time or until defrost thermostat
reopens at approximately 65° F (18° C) coil
temperature of liquid line.
fan−motor lead to OF2 on control board (refer to
Figure 12).
Defrost Control Board
H9C1
®
O1
C
US
OF1
K1
OF2
C19
C9
C1
1
DFT
Y
P2
T1 C C O
O
R
W
2
Y
C
sure setpoint is below indoor ambient temperature
to call for cooling, or above indoor ambient to call
for heating.
HEAT. Operate unit for minimum 15 minutes, then
check the system refrigerant charge.
otherwise,
1
U1
C17
1
R20
P3
J2
1
W1
30 60 90
J1
P1
1
1
SPEEDUP
11
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