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Mitsubishi Electric Mini-Split Code U9

Soft lockout

Power supply abnormality - overvoltage, undervoltage, overcurrent or a bad power synchronous signal. The PFC circuit saw DC bus voltage rise to 430 V, drop to 200 V, or input current fall out of range.

Manual wording: “PFC error (Overvoltage/Undervoltage/Overcurrent) - PFC detected any of the following: a) Increase of DC bus voltage as follows: 430 V”

Documented for: PUZ-HA and other A-Control outdoor units

Likely causes, most common first

  1. Abnormal increase in power source voltage
  2. Decrease in power source voltage or an instantaneous drop
  3. Disconnection or loose connection of the compressor wiring
  4. Misconnection of the reactor (DCL)
  5. Defective outdoor power circuit board
  6. Defective reactor (DCL)
  7. Disconnection or loose connection of CN2 between the outdoor power board and the controller board

What you can safely check yourself

  • Check whether the house has had a power flicker, brownout or storm outage recently
  • Check that the breaker feeding the outdoor unit is on and has not tripped
  • Turn the system off at the breaker, wait one minute, and turn it back on once

When to call a technician

Measuring supply voltage at the unit and testing the reactor and power board are technician tasks. If the whole house has voltage problems, that is an electrician's call.

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

Source

Other Mitsubishi Electric codes