HVAC Code Lookup

Mitsubishi Electric Mini-Split Code U5

Soft lockout

Abnormal temperature of the heatsink. The heatsink thermistor TH8 read 170F (HA24) or 177F (HA30/36/42) or higher, meaning the inverter electronics are overheating.

Manual wording: “Temperature of heatsink - Abnormal if heat sink thermistor(TH8) detects temperature indicated below. HA24: 170F [77C], HA30/36/42: 177F [81C]”

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

Likely causes, most common first

  1. The outdoor fan motor is not running
  2. Failure of the outdoor fan
  3. Airflow path is clogged
  4. Rise of ambient temperature around the outdoor unit
  5. Defective thermistor
  6. Defective input circuit on the outdoor power circuit board

What you can safely check yourself

  • Check that the outdoor unit has clear air space around it and is not blocked by fencing, plants, stored items, snow or leaves
  • Check that the outdoor fan is spinning when the unit runs
  • Turn the system off at the breaker, wait one minute, and turn it back on once

When to call a technician

If the outdoor unit is clear and U5 returns, the fan motor, thermistor or power board is at fault. 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

Other Mitsubishi Electric codes