In brief
Fault code U7 on Mitsubishi Electric Ecodan PUHZ SW50VKA BS Service Manual OCH525C — ecodan-puhz- means: Fault code U7 indicates a superheat anomaly due to a discharge temperature that is too low. This fault is triggered when the discharge superheat remains at or below -15°C for 3 minutes, despite a minimum opening signal to the linear expansion valve after 10 minutes of compressor operation. Most common cause: The main cause is continuous detection of an abnormally low discharge superheat (≤ -15°C). This can result from a disconnected or loose contact of the discharge temperature thermistor (TH4), a faulty thermistor holder, a defective connection of the linear expansion valve (LEV) coil or connector, or a faulty valve itself. First action: Check that the stop valves are open.. Call a registered engineer if the fault returns after basic checks or involves refrigerant work (F-Gas registered engineer required).
According to the Ecodan PUHZ SW50VKA BS Service Manual OCH525C (p.23), fault code U7 is triggered when the discharge superheat remains at or below -15°C for 3 minutes despite a minimum opening signal to the linear expansion valve after 10 minutes of compressor operation.
U7 • Mitsubishi Electric • Ecodan PUHZ SW50VKA BS Service Manual OCH525C — ecodan-puhz-
Fault code U7 Mitsubishi Electric: causes, diagnosis and solution
Fault code U7 indicates a superheat anomaly due to a discharge temperature that is too low. This fault is triggered when the discharge superheat remains at or below -15°C for 3 minutes, despite a minimum opening signal to the linear expansion valve after 10 minutes of compressor operation.
Source: Mitsubishi Electric documentation (service manual – according to product reference)
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What does fault code U7 on Mitsubishi Electric mean?
Fault code U7 indicates a superheat anomaly due to a discharge temperature that is too low. This fault is triggered when the discharge superheat remains at or below -15°C for 3 minutes, despite a minimum opening signal to the linear expansion valve after 10 minutes of compressor operation.
The main cause is continuous detection of an abnormally low discharge superheat (≤ -15°C). This can result from a disconnected or loose contact of the discharge temperature thermistor (TH4), a faulty thermistor holder, a defective connection of the linear expansion valve (LEV) coil or connector, or a faulty valve itself.
Symptômes
- Display of fault code U7 on the outdoor unit.
- LED indication on the outdoor PC board: 10 flashes of 2.5 seconds followed by 2.5 seconds off.
- Unit stops operating in fault mode.
- Detection of a discharge temperature of 50°C or less for 20 minutes (on some models).
Diagnostic
1. Check connections and electrical components
- Check that the stop valves are open.
- Inspect the connections of the thermistors (TH4, TH34) and the expansion valve terminals (LEV-A, LEV-B) on the outdoor controller board.
- Measure the resistance values between the terminals of the indoor and outdoor linear expansion valves using a tester.
- Check the installation and condition of the discharge temperature thermistor holder (TH4).
2. Inspect the linear expansion valve and circuit
- Check the linear expansion valve coil and its connector.
- Inspect the condition of the linear expansion valve (LEV).
- Check the refrigerant charge in the unit and inspect the refrigerant circuit.
How to reset fault code U7 on Mitsubishi Electric?
First, check that the stop valves are open and that the unit contains the specified refrigerant charge. Then, thoroughly inspect all electrical connections (TH4, TH34, LEV-A, LEV-B) and replace any faulty components such as the thermistor, its holder, or the linear expansion valve if necessary.
When should you call an F-Gas engineer?
This fault occurs during diagnosis of Mitsubishi Electric Ecodan systems presenting a critical discharge temperature. The installer must check the tightness of the stop valves, the refrigerant charge, and the physical integrity of the electrical connections (TH4, TH34, LEV-A, LEV-B).
Affected models
- Ecodan PUHZ SW50VKA BS
- Ecodan PUHZ HW140VHA2 BS
- Ecodan PUHZ HW140YHA2 BS
- Ecodan ATW PUHZ W50VHA BS
- MUYTP3550VFS
Field context
This fault occurs during diagnosis of Mitsubishi Electric Ecodan systems presenting a critical discharge temperature. The installer must check the tightness of the stop valves, the refrigerant charge, and the physical integrity of the electrical connections (TH4, TH34, LEV-A, LEV-B).
Technical source data
Code U7 signals an abnormally low discharge superheat (≤ -15°C for 3 min) despite a minimum opening signal to the linear expansion valve (LEV) after 10 min of compressor operation. Priority causes include a disconnected or loose contact of the discharge temperature thermistor (TH4), a faulty holder, or LEV connection/circuit issues (coil, connectors LEV-A/LEV-B). It is essential to check the thermistor installation, component resistance, and the condition of the valve itself. (Sources: Ecodan PUHZ SW50VKA BS Service Manual OCH525C p.23, Ecodan PUHZ HW140VHA2 BS Service Manual OCH439N p.56, Ecodan ATW PUHZ W50VHA BS Service p.17)
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) · MUYTP3550VFServicemanualOBH817C — muytp3550vfservicemanualobh817c.pdf (p. 24)
Questions fréquentes
What are the exact conditions for triggering fault code U7?
Code U7 is triggered when the discharge superheat is continuously detected at -15°C or below for 3 minutes. This anomaly is recorded only if the linear expansion valve (LEV) receives a minimum opening signal after the compressor has been running for at least 10 minutes. (Sources: Ecodan PUHZ SW50VKA BS Service Manual OCH525C p.23, Ecodan PUHZ HW140VHA2 BS Service Manual OCH439N p.56)
What initial checks should be carried out before suspecting a faulty component?
Before inspecting electrical connections or the valve, check that the stop valves are fully open and that the unit contains the specified refrigerant charge. Then, thoroughly inspect all electrical connections of the discharge thermistor (TH4), the TH4 holder, as well as the coil and connector connections of the linear expansion valve (LEV-A and LEV-B).
How do I check the integrity of the linear expansion valve (LEV)?
The procedure involves measuring the resistance values between the terminals of the linear expansion valve and the indoor valve using a multimeter. If abnormal values are detected or if the valve is faulty, it must be replaced. For some models, it is also necessary to specifically check the LEV coil according to the component inspection procedures.
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