Unit Sequence Of Operations - Lennox XC20-036-230-01 Installation And Service Procedure

Unit Sequence of Operation
The following figures illustrate the overall unit sequence of operation along with the operation of various pressure switches
and temperature sensors. The figures also illustrate the use of the compressor anti-short-cycle function in relation to unit
Status, unit Fault and lockout LED Codes and unit system operation interactions.
On 24 VAC power-up or outdoor reset, the outdoor control shall perform the following tasks:
Start the anti-short cycle 3-minute delay in the outdoor control.
1.
Check status of the temperature sensor and pressure devices.
2.
If the outdoor control does not detect any error codes, outdoor control sends 24 volts out on the
3.
CNTCTR terminals to pull in the contactor coil. (Note - These checks take about 60 seconds.)
The contactor contacts pull IN and main power is applied to the compressor inverter.
4.
No
XC20
From idle mode
Room thermostat sends a cooling percentage of
maximum capacity demand to the main control
board in the outdoor unit.
Yes
All switches closed
and sensors in operat­
ing range.
Yes
Outdoor Control
1. Sends a demand to the compressor
inverter to start and run the
compressor up to the requested
pumping capacity (Frequency in
hertz).
2. Outputs a DC voltage on the DAN
PWM and COM terminals to start
and run the outdoor fan motor at the
demand RPM.
3. Sends a communication signal into
the indoor unit to start and run the
supply fan motor at the demand air
volume (CFM).
Figure 27. 24 Volt Power-Up or Outdoor Reset
Check for status or
fault codes in the
outdoor control or
No
room thermostat.
(NOTE - Refer to low
pressure and high
pressure switch flow
charts for sequence
of operation.
Diagnostic Screen
1. View the AIR CONDITIONING 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.
50