HP - A 10
Sequence Of Operation
Defrost initiation from second stage heating cycle
When the system is operating in second stage heating and the
control initiates a defrost cycle, the control simultaneously
de-energizes the PWM signal to the outdoor fan motor
while energizing the SOV solenoid coil to the cooling mode
position. The control also sends a demand message to the
indoor unit to run the blower at 2
nd
stage cooling speed and
energize auxiliary heat (if equipped). Auxiliary heat blower speed
may be higher than 2
nd
stage compressor blower speed and will
take precedence during defrost. The Y1 and Y2 LEDs will be
ON. The EEV will drive to ½ open based on the presence of
a 24 volt AC signal to J6/O.
Defrost termination to second stage heating cycle
When the control senses that the coil temperature has risen
to the programmed termination temperature or that the maximum
15 minute override has expired, the control will send a high
speed PWM signal to re-energize the outdoor fan motor.
There is a 12 second time delay (soft switchover) before de-
energizing the SOV solenoid coil back to the heating mode
position. At the same time, a demand message will be sent to
the indoor unit to de-energize auxiliary heat. The Y1and Y2
LED will remain ON and the EEV control will send the
necessary pulse signals to the stepper motor coil returning
the valve to second stage heating position and begin monitoring
superheat. The system will stay in the defrost cycle if the comfort
control demand changes from second to first stage capacity
request however; the system will shut down if the comfort
control demand message for first stage capacity ends. The
system will continue the current defrost cycle the next time the
comfort control sends a demand message for compressor
heat.
Refer to the schematic diagram on page 7
20 SEER Sequence of Operation
2
6
7
14
2
8
19
27
2
6
7
14
8
15
19
1
Depending on the load in the structure, at the end of a defrost
cycle, the system could do one of the following:
1. Comfort control demand could be satisfied and turn off the
equipment.
2. Comfort control demand could request the system to run 1
st
stage heating mode (1 minute stage delay enforced).
3. Comfort control demand could request the system to run 2
nd
stage heating mode.
4. Comfort control demand could request the system to run 3
rd
stage heating mode.
a. For heat pump systems with electric auxiliary heat,
this is 2
nd
stage compressor with 1
st
stage auxiliary
heat energized.
b. For dual fuel systems, this is 2
nd
stage compressor
heat when outdoor temperatures are above the
compressor lockout temperature or 2
nd
stage gas
furnace (3-stage furnace) below the compressor
lockout temperature.
5. Comfort control demand could request the system to run 4
th
stage heating mode.
a. For heat pump systems with electric auxiliary heat,
this is 2
nd
stage compressor with 2
nd
stage auxiliary
heat energized (2
nd
and 3
rd
stage aux heat will both be
energized in this case, if equipped)
b. For dual fuel systems, this is 2
nd
stage compressor
heat when outdoor temperatures are above the
compressor lockout temperature or 3
rd
stage gas
furnace (3-stage furnace) below the compressor
lockout temperature.
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