HVAC Code Lookup

Mitsubishi Electric Mini-Split Code U1

Soft lockout

Abnormal high pressure. The 63H high pressure switch opened at 602 PSIG during compressor operation, so the system shut down. Something is stopping the system from rejecting heat.

Manual wording: “High pressure (High pressure switch 63H worked) - Abnormal if high pressure switch 63H worked during compressor operation. *4.15 MPa [602PSIG]”

Documented for: A-Control outdoor units (PUZ, MUZ, MXZ)

Likely causes, most common first

  1. Short cycle of the indoor unit - supply air recirculating back into the return
  2. Clogged filter on the indoor unit
  3. Decreased airflow from a dirty indoor fan or dirty indoor heat exchanger
  4. Locked or malfunctioning indoor fan motor
  5. Stop valve not fully open
  6. Clogged or broken pipe
  7. Locked or malfunctioning outdoor fan motor
  8. Short cycle of the outdoor unit or dirty outdoor heat exchanger
  9. Disconnection or contact failure of the 63H connector on the outdoor controller board

What you can safely check yourself

  • Remove and clean or replace the indoor air filters
  • Clear anything blocking the indoor unit inlet or outlet
  • Check the outdoor unit is clear of snow, ice, leaves, grass clippings and stacked items, with open space all around
  • Turn the system off at the breaker, wait one minute, and turn it back on once

When to call a technician

If the filters and outdoor coil are clean and U1 comes back, the refrigerant circuit, a fan motor or a stop valve is at fault. Never jumper the 63H switch. Call a technician.

A Mitsubishi Electric mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.

Source

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