In brief

Fault code UD on Mitsubishi Electric Ecodan PUHZ SW50VKA BS Service Manual OCH525C — ecodan-puhz- means: Fault code Ud on Mitsubishi Electric Ecodan systems indicates overheating protection triggered when the liquid thermistor (TH3) or pressure sensor (63HS) detects a temperature of 70°C or higher during compressor operation. Most common cause: The main cause is a faulty outdoor fan (motor or short circuit) leading to a short cycle, or a failure of the TH3 thermistor, outdoor controller board, or pressure sensor. First action: Isolate the power supply and then restore it to check if the code persists.. Call a registered engineer if the fault returns after basic checks or involves refrigerant work (F-Gas registered engineer required).

According to the Ecodan ATW PUHZ W50VHA BS Service manual (page 19), the Ud fault code is triggered when the liquid thermistor (TH3) or pressure sensor (63HS) detects a temperature of 70°C or higher during compressor operation.

UD • Mitsubishi Electric • Ecodan PUHZ SW50VKA BS Service Manual OCH525C — ecodan-puhz-

Fault code UD Mitsubishi Electric: causes, diagnosis and solution

Fault code Ud on Mitsubishi Electric Ecodan systems indicates overheating protection triggered when the liquid thermistor (TH3) or pressure sensor (63HS) detects a temperature of 70°C or higher during compressor operation.

Source: Mitsubishi Electric documentation (service manual – according to product reference) · Updated on 16 June 2026

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What does fault code UD on Mitsubishi Electric mean?

The main cause is a faulty outdoor fan (motor or short circuit) leading to a short cycle, or a failure of the TH3 thermistor, outdoor controller board, or pressure sensor.

Symptômes

Display of fault code Ud on the indoor unit.
Compressor shutdown due to thermal protection.
Flashing of the outdoor PC board LEDs (6 times for 2.5 seconds, 2.5 seconds off).
Condenser or liquid temperature exceeding 70°C.
Outdoor unit failure mode recall function activated.

Diagnostic

1. Initial check and safety

Isolate the power supply and then restore it to check if the code persists.
If code U4 is displayed, follow the dedicated resolution procedure for code U4.

2. Inspection of air circuit and components

Check the outdoor unit airflow and for any blockages.
Inspect the outdoor fan condition and measure the pressure via the microprocessor (SW2).

3. Check connections and refrigerant circuit

Verify the opening of stop valves and the tightness of the refrigerant circuit.
Measure the resistance values between the compressor terminals and check the electrical connections.

How to reset fault code UD on Mitsubishi Electric?

Start by checking the outdoor unit airflow and ensure the fan is operating correctly. If the problem persists, check the refrigerant circuit tightness, the opening of stop valves, and the condition of electrical components (TH3 thermistor, pressure sensor, controller board).

When should you call an F-Gas engineer?

This code mainly occurs during cooling mode when the outdoor unit cannot effectively dissipate heat, causing a critical rise in liquid temperature or condensation temperature detected by the TH3 and 63HS sensors.

Affected models

Ecodan PUHZ SW50VKA BS
Ecodan ATW PUHZ W50VHA BS
Ecodan PUHZ HW140VHA2 BS
MUYTP3550VF

Field context

Technical source data

The Ud fault code on Mitsubishi Electric Ecodan systems triggers overheating protection when the liquid thermistor (TH3) or pressure sensor (63HS) detects a temperature of 70°C or higher during compressor operation. Identified causes include a faulty outdoor fan (motor or short circuit) causing a short cycle, a failure of the TH3 thermistor, pressure sensor, or outdoor controller board. The diagnostic procedure recommends first checking the outdoor unit airflow, then performing a restart (power off/on). If the code persists, check the pressure via the microcomputer monitoring function (SW2) and examine the refrigerant circuit tightness and stop valve opening. (Sources: Ecodan ATW PUHZ W50VHA BS Service p.19, Ecodan PUHZ SW50VKA BS Service Manual OCH525C p.25)

Sources: Ecodan ATW PUHZ W50VHA BS Service — ecodan-atw-puhz-w50vha-bs-service.pdf (p. 19) · Ecodan PUHZ SW50VKA BS Service Manual OCH525C — ecodan-puhz-sw50vka-bs-service-manual-och525c.pdf (p. 25) · MUYTP3550VFServicemanualOBH817C — muytp3550vfservicemanualobh817c.pdf (p. 24)

Questions fréquentes

Which components should be checked first for a Ud code?

According to the service manuals, the first step is to check the outdoor unit airflow and fan operation. If the problem persists after a restart, inspect the refrigerant circuit tightness, the opening of stop valves, and the electrical condition of the TH3 thermistor, 63HS pressure sensor, and controller board.

How do I use the microcomputer monitoring function to diagnose the Ud code?

To check the pressure via the microcomputer, access the outdoor unit monitoring function using the SW2 switch. This step helps confirm whether the pressure sensor (63HS) reading is consistent with the detected condensation temperature, helping to isolate a sensor failure from actual overheating.

What does the 6-flash LED indication on the outdoor PC board mean?

A 6-flash indication on the outdoor PC board corresponds to fault code Ud, signalling overheating protection. This indicates that the outdoor heat exchanger thermistor (TH3) temperature or the pressure sensor condensation temperature has exceeded the 70°C threshold during compressor operation in cooling mode.

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