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Hitachi Yutaki M & Yutaki S fault 22

Thermistor for outdoor ambient temperature (THM7)

Heat pump

What it means

Outdoor unit sensor fault: outdoor ambient temperature thermistor (THM7) abnormality.

Likely causes

  1. Incorrect wiring
  2. Disconnected wiring
  3. Broken cable
  4. Short circuit

Where to start

  1. Check Status is enabled for Heating Auto On/Off function
  2. Verify Switch-Off Temperature setting (system stops when outdoor temp exceeds this value)
  3. Verify Switch-On Differential setting (differential between previous day average outdoor temp and Switch-Off temperature)

The full answer, free

  • 4 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.

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