ACiQ PC31

What does ACiQ PC31 mean?

PC31 is a system low pressure protection fault. The outdoor pressure switch cuts off the system because the low-side pressure has dropped below 0.13 MPa, and the LED displays the failure code. Low pressure usually indicates a refrigerant shortage or a fault at the low-pressure protector or its wiring.

Symptoms

• PC31 shown on the display
• System cuts off on low-pressure protection
• Weak cooling or heating output
• Possible signs of a refrigerant leak

Common causes

• Low refrigerant charge or a refrigerant leak
• Low pressure protector miswired or faulty
• Broken low-pressure switch (open circuit)
• Refrigerant-system blockage or fault

Diagnostic steps

1. 01

   Check the protector wiring

   Confirm the low pressure protector and main control board are wired correctly; reconnect them if not.

2. 02

   Test the low-pressure switch

   Disconnect the plug and measure the resistance of the low-pressure protector to determine whether it is broken.

3. 03

   Inspect for refrigerant loss

   Have the refrigerant circuit checked for leaks or undercharge, the common cause of low-pressure trips.

4. 04

   Repair and recharge

   Repair any leak and recharge to specification so the low-side pressure returns to a normal range.

When to call a professional

PC31 commonly means a refrigerant shortage, and leak detection, repair, and recharging require EPA certification and recovery equipment; pressure-switch testing happens around the outdoor unit's high-voltage electronics. Always contact a licensed HVAC technician for PC31; refrigerant work and protector diagnosis must be carried out by a qualified professional, never attempted without certification.