Lennox MPA012S4S-1L Service Manual page 237

Low Pressure Connection
Refrigerant is not enough. Add the refrigerant.
Is the wiring between the low pressure switch and
main control board is connected properly.
Is the low pressure protector broken?
Method: Disconnect the plug. Measure the resistance
of the low pressure protector, if the protector is normal
the value is o,
Check whether the outdoor ambient temperature is to
low.
Check whether the high pressure valve is opened.
Check if the indoor fan runs properly in cooling mode.
Replace outdoor main board.
No
Yes
Yes
No
Yes
Yes
No
Connect it properly..
No
Replace low pressure protector.
Yes
Stop the unit.
No
Fully open the high pressure valve.
Refer to the solution of fan speed mal-
No
function (E8). Find out the cause correct
it.
Lennox Mini-Split Service Manual / Page 237