PC 31 error code

What triggers it

System low pressure protection; the low-pressure switch cuts off the system below 18.85 PSI/0.13MPa.

What to do

1. Check low-pressure protector/main-board wiring and reconnect if incorrect.
2. Measure low-pressure protector resistance and replace the protector if resistance is abnormal.
3. Check whether outdoor ambient temperature is too low and stop the unit if it is.
4. Check that the high-pressure valve core is fully open and that the indoor fan runs properly in cooling mode.
5. Replace the outdoor main board; if pressure remains low after adding refrigerant, check the refrigerant system.

Which systems show it

• MRCOOL DIY 5th Generation single-zone 9k, 12k, 18k, 24k, and 36k D25 indoor/outdoor models listed in manual section 1.1.

Related codes

Technician scope

Technician-tier outdoor auxiliary board diagnostic; see service manual section 4.3

Source

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