UH • Mitsubishi Electric
Fault code UH Mitsubishi Electric: causes, diagnosis and solution
Fault code UH indicates an abnormal current sensor reading or input current error detected by the system during compressor operation. This error occurs when the sensor detects an abnormal value, either between -1.0 A and 1.0 A, or an input current exceeding 40 A (or 37 A for 10 seconds).
Proof status : Manufacturer reference needed for the exact range
Source: Mitsubishi Electric documentation (service manual – according to product reference)
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Founder of AskMarcel.app. Sheets are written from manufacturer documentation; the reference is shown when it has been verified.
In brief
Fault code UH on Mitsubishi Electric means: Fault code UH indicates an abnormal current sensor reading or input current error detected by the system during compressor operation. This error occurs when the sensor detects an abnormal value, either between -1.0 A and 1.0 A, or an input current exceeding 40 A (or 37 A for 10 seconds). Most common cause: The main cause is abnormal current detection by the sensor, typically resulting from disconnection or poor connection of the compressor cables (phases U, V, W), a drop in supply voltage, a refrigerant leak, or a faulty circuit on the outdoor power PCB. First action: Check for disconnection, looseness, or reversed connection of compressor cables.. Call a registered engineer if the fault returns after basic checks or involves refrigerant work (F-Gas registered engineer required).
According to the Mitsubishi Electric service manual for the Ecodan PUHZ SW50VKA BS, the UH fault code triggers if the current sensor detects a value between -1.0 A and 1.0 A or an input current of 40 A (or 37 A for 10 seconds) during compressor operation.
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What does fault code UH on Mitsubishi Electric mean?
Fault code UH indicates an abnormal current sensor reading or input current error detected by the system during compressor operation. This error occurs when the sensor detects an abnormal value, either between -1.0 A and 1.0 A, or an input current exceeding 40 A (or 37 A for 10 seconds).
The main cause is abnormal current detection by the sensor, typically resulting from disconnection or poor connection of the compressor cables (phases U, V, W), a drop in supply voltage, a refrigerant leak, or a faulty circuit on the outdoor power PCB.
Symptoms
- Fault code UH displayed (9 flashes, 2.5 seconds OFF according to some manuals).
- Compressor stops or system shuts down.
- Input current outside normal range (excluding test run).
- Detection of zero or very low current (-1.0 A to 1.0 A) during operation.
Diagnosis
1. Check connections and wiring
- Check for disconnection, looseness, or reversed connection of compressor cables.
- Correct the wiring of phases U, V and W to the compressor by referring to the test point diagram on the outdoor power PCB.
2. Electrical and refrigeration measurements
- Check the supply voltage and the condition of the electrical installation.
- Check that the stop valves are open and that there is no short circuit in the outdoor unit air duct.
- Check for refrigerant leak or shortage.
Repair and return to service — Mitsubishi Electric fault UH
First correct the compressor wiring (phases U, V, W) ensuring there is no disconnection or reversal. If the wiring is correct, check the supply voltage and the condition of the refrigeration circuit. If the fault persists, replace the outdoor power PCB.
When should you call an F-Gas engineer?
Contact an F-Gas registered engineer if the fault returns after basic checks, involves refrigerant charging, or requires PCB or compressor replacement on Mitsubishi Electric.
Affected models
- Ecodan PUHZ SW50VKA BS
- Ecodan ATW PUHZ W50VHA BS
- MUYTP3550VFS
- Ecodan PUHZ HW140VHA2 BS
- Ecodan PUHZ HW140YHA2 BS
Field context
This code occurs during compressor start-up or operation when the system cannot measure a valid current (zero or too high). It is frequently encountered due to loose terminals on the compressor, phase loss, mains voltage drop, or mechanical seizure.
Frequently asked questions
What are the current thresholds that trigger fault code UH?
Fault code UH triggers if the sensor detects an abnormal current between -1.0 A and 1.0 A during compressor operation. Additionally, a value of 40 A, or a value of 37 A or more maintained for 10 consecutive seconds, also causes this fault. Note that this error is ignored during start-up tests (test run).
What is the first diagnostic step for fault code UH?
The first action is to correct the compressor wiring (phases U, V, W). Check that there is no disconnection or phase reversal. It is essential to refer to the specific test point diagrams in the service manual (e.g., section 8-6 or 10-9 depending on the model) to confirm continuity and polarity before proceeding with other checks.
Should the outdoor power PCB be replaced immediately?
No. Although a faulty sensor circuit on the outdoor power PCB is a possible cause, the procedure requires first checking the compressor wiring, supply voltage, and refrigerant leak. Replacement of the outdoor power PCB is only recommended after confirming that the wiring is correct and that other causes (voltage, refrigerant) have been ruled out.
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