Service Manual

15
OF2
HK32EA003
O
F1
ON
QUIET SHIFT
120
30 60
60 30
90
INTERVAL TIMER
OFF
P3
DFT
O R W
2
Y C
T2 C C O
DFT
T1 Y
P1
J1
SPEEDUP
Speedup
Pins
Defrost interval
DIP switches
Quiet
Shift
A05378
Fig. 9 – 1174185 Defrost Control
Quiet Shift (
Fast # 1174185)
This control has the option of shutting down the compressor
for 30 seconds going in and coming out of defrost. This is
accomplished by turning DIP switch 3 to the ON position.
Factory default is in the OFF position. Enabling this feature
eliminates occasional noise complaints associated with
switching into and out of defrost.
Five - Minute Compressor Delay (
Fast # 1174185)
This control features a 5- minute time delay to protect the
compressor from short cycling. The delay begins counting
when the low voltage is interrupted, and at the end of
heating or cooling cycle.
System function and Sequence of operation
(Fast # 1174185)
On power- up (24 volts between R- C) the 5 minute cycle
timer begins counting down. The compressor will not be
energized until this timer is elapsed.
Cooling
On a call for cooling, thermostat makes R- O, R- Y, and
R- G. Circuit R- O energizes reversing valve switching it to
cooling position. Circuit R- Y sends low voltage through the
safeties and energizes the T1 terminal on the circuit board.
If the compressor has been off for 5 minutes, or power has
not been cycled for 5 minutes, the OF2 relay and T2
terminal will energize. This will close the contactor, start the
outdoor fan motor and compressor.
When the cycle is complete, R- Y is turned off and
compressor and outdoor fan should stop. When using ICP
thermostats, the reversing valve remains energized in the
cooling mode until the thermostat is switched to heat, or the
mode it turned off. The 5- minute time guard begins
counting. Compressor will not come on again until this time
delay expires. In the event of a power interruption, the time
guard will not allow another cycle for 5 minutes.
Heating
On a call for heating, thermostat makes R- Y, and R- G.
Circuit R- Y sends low voltage through the safeties and
energizes the T1 terminal on the circuit board. T1 energizes
the defrost logic circuit. If the compressor has been off for 5
minutes, or power has not been cycled for 5 minutes, the
OF2 relay and T2 terminal will energize. This will close the
contactor, start the outdoor fan motor and compressor.
When the cycle is complete, R- Y is turned off and the
compressor and outdoor fan should stop. The 5 minute time
guard begins counting. Compressor will not come on again
until this time delay expires. In the event of a power
interruption, the time guard will not allow another cycle for 5
minutes.
Defrost
Sequence
The defrost control is a time/temperature control that has
field selectable settings of 30, 60, 90 and 120 minutes.
These represent the amount of time that must pass after
closure of the defrost thermostat before the defrost
sequence begins.
The defrost thermostat senses coil temperature throughout
the heating cycle. When the coil temperature reaches the
defrost thermostat setting of approximately 32 degrees F, it
will close, which energizes the DFT terminal and begins the
defrost timing sequence. When the DTF has been
energized for the selected time, the defrost cycle begins. If
the defrost thermostat opens before the timer expires, the
timing sequence is reset.
Defrost cycle is terminated when defrost thermostat opens
(~65 degrees) or automatically after 10 minutes.
Deluxe Defrost
Speedup
To initiate a force defrost, speedup pins (J1) must be
shorted with a flat head screwdriver for 5 seconds and
RELEASED. If the defrost thermostat is open, a short
defrost cycle will be observed (actual length depends on
Quiet Shift switch position). When Quiet Shift is off, only a
short 30 second defrost cycle is observed. With Quiet Shift
ON, the speed up sequence is one minute; 30 second
compressor off period followed by 30 seconds of defrost
with compressor operation. When returning to heating
mode, the compressor will turn off for an additional 30
seconds and the fan for 40 seconds.
If the defrost thermostat is closed, a complete defrost cycle
is initiated. If the Quiet Shift switch is turned on, the
compressor will be turned off for two 30 second intervals as
explained previously.
Troubleshooting (Fast # 1174185)
If outdoor unit will not run:
1. Does the Y input have 24 volts from thermostat? If
not, check thermostat or wire. If yes proceed to #2
2. The Y spade terminal should have 24 volts if Y input
is energized. This output goes through the pressure
switches and back to the T1 input to energize the time
delay and defrost timing circuit. If the contactor is not
closed, the time delay may still be active. Defeat time
delay by shorting speed up pins for 1 second. Be sure
not to short more than 1 second.
3. Once time delay has elapsed voltage on T2 should
energize contactor with 24v. Check voltage on
contactor coil. If no voltage is present, check for
opened pressure switch.
4. If voltage is present and contactor is open, contactor
may be defective. Replace contactor
5. If contactor is closed and unit will still not run, check
capacitor and compressor.
If unit will not go into
defrost:
1. Perform speedup function as described above to test
the defrost function of the circuit board.
2. If the unit will go into defrost with the speed up, but
will not on its own, the defrost thermostat may not be
functioning properly. Perform the full defrost
thermostat and board troubleshooting the same as
described for the FAST # 1173636 / 1177927 control.
Other than the Quiet shift (if selected), and the
speedup timing, the troubleshooting process is
identical.