Aiwa -09CHSRINV/TP11 Service Manual page 54

3.2.16 F4---Cooling system Gas flow abnormal protection
When compressor startup, unit will check the variation of IDU coil temperature. If there is mistake installer forgetting
to open the 2-way or 3-way valve on ODU, the gas can't flow in the cooling system, it will show F4 protection.
Air Conditioner Service Manual
Start
Display F4
Check the 2-way
valve and 3-way No
valve opened？
No
No The IPT sensor
open or short?
Yes
Replace the sensor
End
Yes
Open the valve
F4 disappear?
No
Yes
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