U1 • Gree
Gree fault code U1: causes, diagnosis and solution
Fault code U1 indicates a failure of the phase current detection circuit for the compressor. This fault, classified as a hardware failure, causes the compressor to stop to protect the system.
Proof status : Manufacturer reference needed for the exact range
Source: Gree 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 U1 on Gree means: Fault code U1 indicates a failure of the phase current detection circuit for the compressor. This fault, classified as a hardware failure, causes the compressor to stop to protect the system. Most common cause: The main cause is the detection of an average offset voltage exceeding 12.5% of 1.65 V on the current detection circuit or the current sensor itself. First action: Observe the display of code U1 on the remote controller or Nixie tube after a 200-second wait.. Call a registered engineer if the fault returns after basic checks or involves refrigerant work (F-Gas registered engineer required).
According to the Flexx Ultra R32 service manual (page 52), the system judges the fault if the average offset voltage exceeds 12.5% of 1.65 V within 1 second of power-up.
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What does fault code U1 on Gree mean?
Fault code U1 indicates a failure of the phase current detection circuit for the compressor. This fault, classified as a hardware failure, causes the compressor to stop to protect the system.
The main cause is the detection of an average offset voltage exceeding 12.5% of 1.65 V on the current detection circuit or the current sensor itself.
Symptoms
- Display of code U1 on the remote controller or Nixie tube after 200 seconds.
- Compressor stops during cooling and dehumidification cycles, while the indoor fan continues to run.
- Complete unit shutdown during heating cycles.
- Indicator flashing (ON 0.5s / OFF 0.5s) on some models.
Diagnosis
1. Check the code and system behaviour
- Observe the display of code U1 on the remote controller or Nixie tube after a 200-second wait.
- Check system behaviour: the compressor should stop in cooling mode (indoor fan active) and the entire unit should stop in heating mode.
2. Analyse the detection circuit
- Confirm that the average offset voltage exceeds 12.5% of 1.65 V within 1 second of power-up.
- Identify the fault as being in the current detection circuit or the current sensor.
Repair and return to service — Gree fault U1
Replace the outdoor control board AP1. This part contains the faulty current detection circuit identified as the probable cause in the service manuals.
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 Gree.
Affected models
- Sapphire Service Manual 18MBH/24MBH
- Multi21 Plus 18K/24K
- Flexx Ultra R32
- High Static Slim Duct
- Universal Floor Ceiling
- Livo Plus 30K/36K
Field context
This code appears during a start-up attempt or during operation, preventing the compressor from running. The outdoor unit LED indicator flashes or displays the code, and the indoor fan behaviour varies by mode (cooling or heating) to indicate the state.
Frequently asked questions
What is the exact behaviour of the unit when code U1 is active?
When code U1 is displayed, the compressor stops immediately to protect the system. Depending on the operating mode: in cooling or dehumidification, the indoor fan continues to run while the compressor is inactive. In heating mode, the entire unit shuts down completely. This behaviour is observed on the affected Gree models.
What is the precise technical condition that triggers this fault?
Fault U1 is triggered if, after power-up, the average offset voltage detected on the current circuit or sensor exceeds 12.5% of 1.65 V within 1 second. This condition indicates a hardware failure of the current detection circuit or the sensor itself, requiring intervention on the control board.
What is the recommended repair solution for this code?
The repair procedure is to replace the outdoor control board AP1. This component contains the current detection circuit identified as the cause. No other circuit tests are specified in the service manuals to resolve this offset voltage detection issue.
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