In brief
Fault code U5 on Mitsubishi Electric Ecodan PUHZ SW50VKA BS Service Manual OCH525C — ecodan-puhz- means: Fault code U5 indicates an abnormal heat sink temperature detected by thermistor TH8, exceeding model-specific thresholds (e.g., 77°C or 84°C). This signal may also originate from a voltage anomaly according to some manual references. Most common cause: The main cause is a blocked outdoor fan motor, obstructed airflow, excessive ambient temperature, or a failure of thermistor TH8 and its associated circuits. First action: Check if the outdoor fan motor is blocked or if the airflow is obstructed.. Call a registered engineer if the fault returns after basic checks or involves refrigerant work (F-Gas registered engineer required).
According to Mitsubishi Electric service documentation, fault code U5 is triggered when heat sink temperature exceeds model-specific thresholds ranging from 77°C to 95°C.
U5 • Mitsubishi Electric • Ecodan PUHZ SW50VKA BS Service Manual OCH525C — ecodan-puhz-
Fault code U5 Mitsubishi Electric: causes, diagnosis and solution
Fault code U5 indicates an abnormal heat sink temperature detected by thermistor TH8, exceeding model-specific thresholds (e.g., 77°C or 84°C). This signal may also originate from a voltage anomaly according to some manual references.
Source: Mitsubishi Electric documentation (service manual – according to product reference)
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What does fault code U5 on Mitsubishi Electric mean?
Fault code U5 indicates an abnormal heat sink temperature detected by thermistor TH8, exceeding model-specific thresholds (e.g., 77°C or 84°C). This signal may also originate from a voltage anomaly according to some manual references.
The main cause is a blocked outdoor fan motor, obstructed airflow, excessive ambient temperature, or a failure of thermistor TH8 and its associated circuits.
Symptômes
- Display of fault code U5 on the indoor unit.
- System shutdown of the air conditioning.
- Monitoring of a heat sink temperature above the normal limit.
- Possible display of fault code U4 if the problem persists after restart.
Diagnostic
1. Initial and environmental check
- Check if the outdoor fan motor is blocked or if the airflow is obstructed.
- Confirm that the ambient temperature does not exceed the 46°C limit.
2. Restart test and electrical check
- Isolate the power supply, then restore it and check if fault code U5 reappears within 30 minutes.
- Check the resistance value of thermistor TH8 or the temperature via the microcomputer (service tool).
3. Circuit diagnosis
- Inspect the input circuit of the outdoor power board and the fan control circuit.
- Check the connection of connector TH3 on the outdoor control board if a voltage anomaly is suspected.
How to reset fault code U5 on Mitsubishi Electric?
If the air and fan checks are normal, replace thermistor TH8. In case of persistent failure, replace the outdoor power board, then the outdoor control board if necessary.
When should you call an F-Gas engineer?
This code occurs during outdoor unit operation when thermistor TH8 detects a critical heat sink temperature, indicating a risk of compressor overheating or cooling system failure.
Affected models
- Ecodan PUHZ SW50VKA (SW40/50)
- Ecodan PUHZ W50VHA / W85VHA
- Ecodan PUHZ HW140VHA / HW140YHA
- Ecodan PUHZ HW140VHA2 / HW112YHA2
Field context
This code occurs during outdoor unit operation when thermistor TH8 detects a critical heat sink temperature, indicating a risk of compressor overheating or cooling system failure.
Technical source data
Fault code U5 signals an abnormal heat sink temperature (TH8) exceeding model-specific thresholds: 77°C for W50V/W85V and W50VHA ranges, 84°C for SW40/50 and HW140VHA, 89°C for HW140VHA2 (R1-R7), and 91°C/95°C for YHA variants (HW112YHA, HW140YHA and their revisions R1-R7). Causes include a blocked or faulty outdoor fan motor, obstructed airflow, excessive ambient temperature (>46°C), or defects in thermistor TH8, the power board input circuit, or the fan control circuit. A voltage anomaly (Extract 4) can also trigger this code. To diagnose, check the fan, airflow path and TH8 resistance before replacing the power or control board. (Sources: Extract 1, 2, 3, 4, 5)
Sources: Ecodan ATW PUHZ W50VHA BS Service — ecodan-atw-puhz-w50vha-bs-service.pdf (p. 17) · Ecodan PUHZ SW50VKA BS Service Manual OCH525C — ecodan-puhz-sw50vka-bs-service-manual-och525c.pdf (p. 23) · Ecodan PUHZ HW140VHA2 BS PUHZ HW140YHA2 BS Service Manual OCH439N — ecodan-puhz-hw140vha2-bs-puhz-hw140yha2-bs-service-manual-och439n.pdf (p. 56)
Questions fréquentes
What are the temperature thresholds that trigger fault code U5 according to the models?
The thresholds vary by range: 77°C for W50V/W85V and W50VHA models; 84°C for SW40/50 and HW140VHA; 89°C for HW140VHA2 (revisions R1 to R7); and 91°C to 95°C for YHA models (HW112YHA, HW140YHA and their revisions). A temperature exceeding these values triggers the alarm.
What is the first diagnostic step before replacing electronic boards?
First check the outdoor fan motor (blocked or faulty), ensure the airflow path is not obstructed and that the ambient temperature does not exceed 46°C. Then measure the resistance of thermistor TH8 or its temperature via the microprocessor. If these are normal, then replace the power or control board.
How can I confirm if fault code U5 is genuine or temporary?
Isolate the power supply to the outdoor unit and then restore it. If fault code U5 reappears within 30 minutes, the fault is confirmed. If fault code U4 appears instead, follow the specific diagnostic procedures for fault code U4.
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