Error Code: PC 31 – System Low Pressure Protection

Error Code: PC 31 – System Low Pressure Protection

What this means:
The outdoor unit has detected that refrigerant pressure has dropped below 0.13 MPa, triggering a low-pressure protection shutdown. This may occur due to refrigerant undercharge, restricted flow, improper valve operation, or a sensor/wiring fault.

Try this first (quick reset):

1. Turn off power to the unit completely.

2. Wait 2 full minutes.

3. Turn it back on and check if the error clears.

• If the error clears — it may have been triggered by temporary conditions.

• If the error persists — continue with the following checks.

Next steps (for technicians):

1. Check wiring between the low-pressure switch and main board:

   • Disconnect the switch and measure resistance.

   • If the resistance is not 0 ohms → replace the low-pressure switch.

   • If normal → continue below.

2. Verify outdoor temperature and valve operation:

   • If ambient temperature is too low, system pressure may drop naturally — wait and retry.

   • Ensure the high-pressure valve is fully open.

   • If not → open it and retry operation.

3. Check indoor airflow (cooling mode):

   • Make sure the indoor fan is running properly.

   • Poor airflow can cause coil freezing and low-pressure errors.

4. Inspect refrigerant charge:

   • If refrigerant is low → recharge and test.

   • If issue persists despite proper charge → replace the outdoor PCB.

What you might need:

• Low-pressure switch

• Outdoor PCB

• Connection wires

• Refrigerant (for recharge)

• Manifold gauges

Helpful tip:
Low-pressure errors are often caused by a slow leak or improper valve setup after installation. Always check refrigerant level and valve positions before replacing hardware.

Click here to view the detailed guide.TS26-INV