As the largest independent Mitsubishi Electric service and repair company in Adelaide South Australia we see a lot of Mitsi units. A common fault we see on Mitsubishi Electric ducted systems is the UF, UP or U6 error code. This fault code commonly represents a fault within the Outdoor Power PCB, Compressor electrical circuit or Compressor bearings. Of these 3 similar error codes, the most common to see is the U6, UP or UF. This will be displayed on your wall controller after the unit tries to run 10 times in a row without success.

• UF – Compressor overcurrent interruption (when compressor locked). Abnormal if overcurrent of DC bus or compressor is detected within 30 seconds after the compressor starts operating.
• U6 – Power module abnormal. Check abnormality by driving the power module in case overcurrent is detected. (UF or UP error condition).
• UP – Compressor overcurrent interruption. Abnormal if an overcurrent DC bus or compressor is detected after the compressor starts operating for 30 seconds.

• Failure of the Power PCB in outdoor unit
• Electrical failure or fusion of Compressor
• Seized bearings in the Compressor
• Disconnected/broken wiring to the compressor
• Closed service valves at outdoor unit
• Low voltage at outdoor unit

Testing your Mitsubishi Electric air conditioner to determine the cause of a U6, UF or UP fault is relatively straight forward if you know what to look for. Below are the main checks to determine what component has caused this fault. These tests are not DIY and will require a Mitsubishi Electric specialist to test correctly.

Disclaimer – Electricity is dangerous and can kill you. The following information is for educational purposes only. Tests must be performed by an authorised service provider or Mitsubishi Electric specialist. Do not try to perform these tests without the proper expertise and qualifications.

• Check for correct voltage at the outdoor unit, 240v or 415v
  • If power feed is incorrect, contact a licensed electrician or SA Power Networks to rectify power supply to unit/property
• Check both outdoor service valves are fully open
  • If valves are shut, open valves
• Check for visual damage to the Outdoor Power PCB. This could include lizard or rodent damage
  • If damage is found replace Power PCB then further test unit operation
• Check for visual damage to the wiring between the Power PCB and the compressor. This could include lizard or rodent damage
  • If damage is found, replace damaged cable
• Check for correct DC voltage to the compressor is equal and correct
  • If DC voltage is incorrect, replace Power PCB
• Check for equal voltage output from the Power PCB diodes using an inverter checker
  • If inverter checker LED’s are unequal, replace Power PCB
• If the voltage and diodes have tested correctly and no visual damage is found, it is likely the compressor bearings have seized
  • The compressor will need to be replaced and the unit further tested

It is important to ensure the correct tests are completed to determine what part requires replacement. It’s an expensive exercise to replace a compressor when only a damaged wire or PCB is to blame. The cost to replace the Power PCB can range from $800.00 – $1,300 depending on the model of your Mitsubishi Electric unit. Compressor replacement cost can vary from $2,500 – $4,000 depending on the model of your Mitsubishi Electric unit. The amount of refrigerant, outdoor unit location, access and labour involved in replacing the compressor will also contribute to higher costs. Ensuring the correct parts are diagnosed is vital to make certain you do not waste money on unnecessary parts.

• UF/U6/UF faults can be caused by similar problems
• Correctly determining the faulty part can save you $1,000
• Using a Mitsubishi Electric specialist will ensure the problem is correctly diagnosed and repaired