GREE                                                                        GMV5E DC INVERTER VRF UNITS SERVICE MANUAL 
    231   
causes phase loss or reverse), it will report this error 
Possible reason: 
■The power supply connected to the unit is incorrect, phase loss or reverse happens 
■Detecting circuit is abnormal 
Troubleshooting: 
 
2.2.4.134 “U4” Lack of refrigerant protection 
Error  display: 
ODU  mainboard,  IDU  wired  controller  and  IDU  receive  light  board  will 
display
 
Error judgment condition and method: 
Check the system high pressure and low pressure through pressure sensor. When the system high 
pressure and low pressure is lower than 5 of outdoor ambient temperature before starting operation, the 
unit will stop for protection. 
Possible reason: 
■Refrigerant charging amount is insufficient; 
■System pipeline is leaked; 
Troubleshooting: 
 
2.2.4.135 “U6” Valve error 
Error  display: 
ODU  mainboard,  IDU  wired  controller  and  IDU  receive  light  board  will 
display