Open/Short of Outdoor Unit Thermistors
Mitsubishi Electric · Mitsubishi PUZ-HA30-36NHA4 Outdoor Unit
What does U3 mean?
An open or short circuit is detected in one or more outdoor unit thermistors (TH3, TH32, TH33, TH6, TH7, and TH8). These sensors are critical for monitoring various temperatures within the outdoor unit's refrigerant circuit and ambient conditions, affecting system control. Open detection for TH3, TH32, TH33, TH6 is inoperative for 10 seconds to 10 minutes after compressor start and 10 minutes after/during defrosting.
Additional Steps
Steps 1–2 are listed in Priority Fix.
- 3
Check the lead wires for thermistors (TH3, TH32, TH33, TH6, TH7, TH8) for any breaks or damage.
- 4
Measure the resistance value of each thermistor (TH3, TH32, TH33, TH6, TH7, TH8) and compare it to expected values for the measured temperature.
- 5
If thermistors and wiring are confirmed correct, replace the outdoor controller circuit board.