HP - A 5
Sequences Of Operation
16 SEER Sequence of Operation
2
8
7
2
15
2
10
2
2
7
9 8
15
1
1
1
2
16
17
Defrost Mode
During the heating cycle, the outdoor coil may become frosted
or iced-up which reduces system capacity. The main control
board determines when the system requires a defrost cycle
using Demand Defrost logic. Two thermistor inputs are used to
compare outdoor ambient temperature to coil temperature. The
Ambient Sensor is located below the control box where the
outside air temperature can be sensed and the Coil Sensor is
located in a copper well attached to one of the lower circuits of
the outside coil. The delta between these sensors is used to
calculate when the outdoor coil is frosted and needs to be
cleared.
Defrost initiation
When a heat pump system is operating in any stage heating and
the control initiates a defrost cycle, 3 and 5 ton controls
remove the PWM signal to de-energizes the outdoor fan motor
and 2 and 4 ton controls de-energized ODF-1 which removes
power from the outdoor fan motor. The compressor will turn
off for 30 seconds and the control energizes the SOV
solenoid coil to the cooling mode position. The control also
sends a demand message to the indoor unit to energize
auxiliary heat (if equipped). Auxiliary heat blower speed may
be higher than compressor blower speed and will take
precedence during defrost. The Y1 and/or Y2 LEDs will be ON.
Defrost termination
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 re-energize
the outdoor fan motor by sending a PWM signal (3 and 5 ton
models) or a 24 volt AC signal from T1 to ODF-1 (2 and 4
ton models). The compressor will turn off for 30 seconds and
the SOV will de-energize back to the heating mode position.
At the same time, auxiliary heat will be de-energized and indoor
airflow will return to compressor airflow, matching the stage
request sent from the Comfort Control. The Y1 and/or Y2
LEDs will be ON depending on what stage is required to meet
the demand of the Comfort Control.
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.
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.
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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