Unit Sequence Of Operations; 24 Vac Power-Up Or Outdoor Reset - Lennox XP25-024-230-01 Installation And Service Procedure

Unit Sequence of Operations

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 lock out LED Codes and unit system operation interactions.
On 24 VAC power-up or outdoor reset, the outdoor control shall perform the follow­
ing 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
3.
out on the 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
Yes
Emer­
gency
Heat Se­
lected?
No
All
switches
closed and
sensors in
operating
range?
Go To Auxiliary
Yes
Heating
Below Low
BP
Balance
Point
Region
Above the Low BP
or Not Applicable
Go To Primary
Heat Pump
Heating
Go To
Modulat­
ing Heat
Pump
Heat
Figure 29.

24 VAC Power-Up or Outdoor Reset

System
Idle
Room
Thermostat
Yes
Demand
Heating
No
Check for status or
fault codes in outdoor
control or room ther­
mostat (Note - Refer to
low pressure and high
pressure switch flow
charts for sequence of
operation).
No
Page 51
Heating or
Cooling
Cooling
All
switches
closed and
sensors in
operating
range?
Yes
Go To
Modu­
lating
Cooling
XP25