WHEN THE COMPRESSOR STARTS UP, THE AC UNIT WILL CHECK THE VARIATION OF THE INDOOR UNIT COIL TEMPERATURE. IF THERE IS A MISTAKE AND IT FORGETS TO OPEN THE 2-WAY OR 3-WAY VALVE ON THE OUTDOOR UNIT, THE GAS CANNOT FLOW IN THE COOLING SYSTEM. WHEN THIS HAPPENS, THE F4 PROTECTION CODE WILL BE DISPLAYED.
REPAIR:
1) CHECK THE CONDITION OF THE 2-WAY AND/OR 3-WAY VALVE
2) CHECK IF THE COOLING SYSTEM IS BLOCKED OR NOT. IF YES, PLEASE REMOVE BLOCKAGE