Defrost Control Board; System Function And Sequence Of Operation - Carrier Residential Air Conditioners and Heat Pumps Application Manualline

14. Remove jumper between DFT and R terminals. Reconnect
defrost thermostat leads. Failure to remove jumper causes
unit to switch to defrost every 30, 60, or 90 minutes and
remain in defrost for full 10 minutes.
15. Replace control box cover. Restore power to unit.
If defrost thermostat does not check out following above items
or incorrect calibration is suspected, check for defective
thermostat as follows:
1. Follow items 1- -5 above.
2. Route sensor or probe underneath coil (or other convenient
location) using thermocouple temperature measuring
device. Attach to liquid line near defrost thermostat. Insulate
for more accurate reading.
3. Turn on power to outdoor unit.
4. Restart unit in heating.
5. Within a few minutes, liquid line temperature drops within a
range causing defrost thermostat contacts to close.
Temperature range is from 33_F to 27_F. Notice
temperature at which ohmmeter reading goes from ∞ to zero
ohms. Thermostat contacts close at this point.
6. Short between the speed- -up terminals using a small slotted
screwdriver.
7. Unit changes over to defrost within 21 sec (depending on
timing cycle setting). Liquid line temperature rises to range
where defrost thermostat contacts open. Temperature range
is from 60_F to 70_F. Resistance goes from zero to ∞ when
contacts are open.
8. If either opening or closing temperature does not fall within
above ranges or thermostat sticks in 1 position, replace
thermostat to ensure proper defrost operation.
NOTE: With timing cycle set at 90 minutes, unit initiates defrost
within approximately 21 sec. When you hear the reversing valve
changing position, remove screwdriver immediately. Otherwise,
control will terminate normal 10- -minute defrost cycle in
approximately 2 sec.
HK32EA003 DEFROST CONTROL
The HK32EA003 defrost control is used in all 25HC Performance
Series heat pumps with Puron refrigerant. Its features include
selectable defrost intervals of 30, 60, 90, & 120 minutes, Quiet
Shift, compressor time delay, deluxe defrost speed up capability.
This section describes the sequence of operation and trouble
shooting methods for this control.
Speedup Quiet
Pins Shift
Fig. 10 – HK32EA003 Defrost Control
Quiet Shift (HK32EA003)
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
HK32EA003
Defrost interval
DIP switches
A05378
the OFF position. Enabling this feature eliminates occasional noise
complaints associated with switching into and out of defrost.
Five- -Minute Compressor Delay (HK32EA003)
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

(HK32EA003)
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 Carrier 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 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.
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