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Hitachi Yutaki M & Yutaki S fault 4

Abnormal transmission between inverter PCB and RASC unit PCB

Heat pump

What it means

Transmission fault between inverter PCB and RASC unit PCB.

Likely causes

  1. Loose connector
  2. Wire breaking
  3. Blowout of fuse
  4. Transmission failure between inverter PCBs

Where to start

  1. Check LED1 (Red) for transmission status between the indoor unit and the unit controller
  2. Check LED2 (Yellow) for transmission status between the indoor unit and the outdoor unit
  3. Check LED3 (Green) for power source status to the PCB

The full answer, free

  • 3 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 337), 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 Hitachi manual for the Yutaki M & Yutaki S. Check the model on the data plate before you order parts.

Other Hitachi Yutaki M & Yutaki S fault codes