Mitsubishi Electric · Heat pumps · Mitsubishi Electric Ecodan PUZ-WM outdoor unit (R32)
U4Open/short of outdoor unit thermistors (TH3, TH34, TH6, TH7, TH8)
Name in the manufacturer's documentation (service manual): Open/short of outdoor unit thermistors (TH3, TH34, TH6, TH7, TH8)
[1]
In plain words (editorial)
Open or short circuit of one of the outdoor unit thermistors (TH3, TH34, TH6, TH7, TH8) – a connector, a thermistor or the controller board.
When to call a service technician: Call the installer.
✎ editorial – written from the cited sources, not a manufacturer statement. Status: draft.
For technicians
Possible causes (source text)
Steps given by the manufacturer (source text)
⚠ Work on refrigerant circuits, mains electricity and PV DC wiring is for qualified technicians only.
The Polish page has more detail (plain-language explanation, safe checks, guides): Read in Polish →
Sources
Every statement has a footnote to the document and PDF page. “Quote verified” means the quote was found automatically in the text of that page.
- [1] Mitsubishi Electric – Service Manual: Air to water heat pump units, outdoor unit PUZ-WM50VHA … PUZ-WM112YAA (OCH727 REVISED EDITION-A, 12/2023) (OCH727A (12/2023)) , p. 26 official manufacturer document quote verified
Open/short of outdoor unit thermistors
- [2] Mitsubishi Electric – Service Manual: Air to water heat pump units, outdoor unit PUZ-WM50VHA … PUZ-WM112YAA (OCH727 REVISED EDITION-A, 12/2023) (OCH727A (12/2023)) , p. 26 official manufacturer document quote verified
(TH3, TH34, TH6, TH7, and TH8)
- [3] Mitsubishi Electric – Service Manual: Air to water heat pump units, outdoor unit PUZ-WM50VHA … PUZ-WM112YAA (OCH727 REVISED EDITION-A, 12/2023) (OCH727A (12/2023)) , p. 26 official manufacturer document quote verified
Defective thermistor
- [4] Mitsubishi Electric – Service Manual: Air to water heat pump units, outdoor unit PUZ-WM50VHA … PUZ-WM112YAA (OCH727 REVISED EDITION-A, 12/2023) (OCH727A (12/2023)) , p. 26 official manufacturer document quote verified
Open/short of outdoor unit thermistors
- [5] Mitsubishi Electric – Service Manual: Air to water heat pump units, outdoor unit PUZ-WM50VHA … PUZ-WM112YAA (OCH727 REVISED EDITION-A, 12/2023) (OCH727A (12/2023)) , p. 26 official manufacturer document quote verified
Check resistance value of TH3, TH34,
- [6] Mitsubishi Electric – Service Manual: Air to water heat pump units, outdoor unit PUZ-WM50VHA … PUZ-WM112YAA (OCH727 REVISED EDITION-A, 12/2023) (OCH727A (12/2023)) , p. 26 official manufacturer document quote verified
Replace outdoor controller circuit board.