View Full Version : Daikin 4mxs 80 fault

28-03-2017, 11:54 AM
Hi I have client and the code on indoor comes up u4 and the flashing light on outdoor means faulty compressor start up the client is a electrican also this job where the fault is, is 200 miles in the middle of know where so need some idea if it's a pcb board
he says the unit does not come on heating or cooling or the compressor does not come on can anyone help

The Viking
28-03-2017, 12:24 PM
Well if he is an electrician, ask him to do an insulation test of the compressor itself and also to check the continuity of its windings.
Then he can also check the output from the inverter with the compressor disconnected.


28-03-2017, 08:09 PM
U4 is a comms error not a compressor fault.

Check you inter-connecting wiring.

Sometimes, the installer runs the comms cable through the high float alarm on the pump so the system stops.

30-03-2017, 09:16 PM
Thanks sorted now the compressor gone