Mitsubishi MU-A24WV

[Kirky]

Hi guys hope everyone is well

Had a call out earlier in the week. A mitsubishi MU-A24WV outdoor MS-A24WV indoor CO split system a/c unit wasnt cooling. On arrival I noticed that a large ball of ice had built up at the outdoor unit. Went inside and the unit had been switched off. The indoor unit was basically a block of ice and the outdoor unit was still running in full cooling steadily making it worse (Not cooling because chocked up with ice). Isolated power supplys to both indoor and outdoor and left to melt the ice. Went back the next day and ran the unit. The outdoor unit will run in full cooling as soon as the power supply is turned on to the indoor. Tried changing modes via the controller to no effect outdoor unit still running in full cooling. I have come across this before and it was simply a stuck contactor however this time contactor is ok. So i replaced the relay still no effect. Im thinking now that the indoor unit control PCB requires changing as there doesnt seem to be any form of control/communication to the outdoor unit which will only turn off if I kill the power to the indoor. A replacement PCB isnt cheap so is there anything else im missing. The unit has been in use for 4 years with no probs, however the customer tells me the outdoor units have been moved recently. Checked for mis-wiring all ok

[lexmark42]

What happens if you disconnect the communications line between indoor and outdoor unit and only leave earth, live, and neutral connected?

With power alone the outdoor unit should not start cooling on itself, should it?

Maybe this could help you:

http://81.3.179.242/workdocs01/Guest...0_00038826.pdf

[sedgy]

hi kirky,
sounds like the contactor is burned out and stuck IN, on the outdoor unit?
sedgy

[Kirky]

Hi

The indoor and the outdoor have seperate power supplys. If I kill the power to the indoor unit the outdoor unit stops running. If the contactor was faulty then with power still on to the outdoor surely the contactor would remain energised. I have inspected the contactor and it seems fine. If the contactor was burnt out and stuck in then if I disconnected the communication wires but left power on then I think the unit would continue to run. I have disconnected the communication wires and the outdoor unit stops. Could a faulty control pcb cause the outdoor unit to constantly cool ?

[lexmark42]

Yes it could. Can you get any error codes out of the indoor unit?

Cheers,
-Dave

[Kirky]

No error codes unit isn't even showing a error via indoor unit LEDs flashing sequence