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Daikin Altherma fault U7-00

Outdoor unit: transmission malfunction between main microcomputer - inverter microcomputer

Heat pump

What it means

Communication abnormality between main and inverter microcomputer.

Likely causes

  1. Faulty main PCB
  2. Faulty inverter PCB
  3. Bad contact between refrigerant loop and inverter heat sink
  4. Lack of refrigerant
  5. Deviation of thermistor (higher temperature measured than actual)
  6. Communication error between bizone PCB and current loop PCB
  7. Main PCB software fault
  8. Main PCB failure

Where to start

  1. Perform a check of the main PCB
  2. Perform a check of the inverter PCB
  3. Refer to '3.16 Main PCB' [>181] for check procedures applicable to the inverter PCB

The full answer, free

  • 7 more checks in order
  • The readings and component tests from the manual
  • How to put it right, step by step
  • The manual page for this fault (page 61), right under the answer
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Safety: Isolate the outdoor unit and any backup heater, and give the inverter capacitors time to discharge before you open the electrics. Anything on the refrigerant circuit needs F-gas certification.

From the Daikin manual for the Altherma. Check the model on the data plate before you order parts.

Other Daikin Altherma fault codes