Lennox MPA009S4S Service Manual page 149

Error Code:
P6
Description: Compressor high-pressure or low-pressure switch open
General Note: If the sampling voltage of pressure switch is not 5V, the LED will display the failure.
Test each pressure switch separately following these flow charts.
Check wiring connections between high pressure
Determine if High pressure switch is faulty.
Method: Disconnect the plug. Measure the resistance
of the high pressure protector, if the protector is normal
Check the outdoor ambient temperature. The outdoor
ambient temperature should not be higher than 50 °C
Check if the outdoor unit ventilation is good
Check if the outdoor fan runs properly
Check outdoor coils. The outdoor unit coils should be
clean and free of any debris.
Replace outdoor main board.
Check whether the refrigerant system is OK.
switch and main PCB.
Yes
the value is 0.
Yes
or 122 °F.
No
Yes
Yes
No
No
No
Make necessary corrections.
No
Replace high pressure protection switch.
Yes
No
Make corrections to allow for proper
No
See Fault code E8 to properly diagnose
outdoor fan motor.
Yes
Clean outdoor coils.
149
Stop the unit.
ventilation