Heat Pump Mode - Lennox XP25-024-230-01 Installation And Service Procedure

On 24 VAC power-up or outdoor reset, the outdoor unit control shall perform the following tasks:
1. Start the anti-short cycle 3 minute delay in the outdoor control.
2. Check status of the temperature sensor and pressure devices.
3. If the outdoor unit control does not detect any error codes, it sends 24 volts out on the CNTCTR terminals to pull
in the contactor coil. (Note - These checks take about 60 seconds).
4. The contact(s) of the contactor pull IN and main power is applied to the compressor inverter.
No
Room thermostat is sending a heating percentage of maximum
capacity demand to the main control board in the outdoor unit.
Outdoor Control
1. Sends a demand to the compressor inverter
to start and run the compressor up to the re­
quested pumping capacity (Frequency in
Hertz).
2. Outputs a DC voltage on the FAN PWM and
COM terminals to start and run the outdoor
fan motor at the desired RPM.
3. Sends a communication signal to the indoor
unit to start and run the supply fan motor at
the demand air volume(CFM).
4. Energizes the on-board reversing valve re­
lay to outputs 24 volts to the reversing valve.
From idle mode
Yes
Yes
All switches closed and
sensors in operating
range.
Yes
Yes
Figure 30. Heat Pump Mode
Page 52
Check for status or fault
codes in outdoor control
or room thermostat.
(Note - Refer to low
No
No
pressure and high pres­
sure switch flow charts
for sequence of opera­
tion.)
Diagnostics Screen
1. View the Heat PUMP screen for
current compressor frequency in
hertz.
2. View the OUTDOOR CONTROL
7-Segment display to read the
RPM of the outdoor fan motor.
3. View the AIR HANDLER screen
for actual CFM of the indoor
blower motor.
XP25