Mitsubishi MSH 26SV issue, what to check and how

[alan_man]

Hi again, I have another split system that I aquired for free from a relative which was replaced approximately a year ago (Unit was in service for about 6 years). It is a Mitsubishi which apparently suffered from compressor failure. The system had the refrigerant reclaimed at time of replacement (was not done by me) and has just sat in storage until now. I was wondering if there was any way to confirm this compressor failure/any specific test for this model that can be done without having the unit connected and up and running? I am not too familiar with the innards of an inverter model but I have tested the cap as well as compressor windings which seem to be ok. There was a small fuse on the PC board that I tested which seemed fine as well. Any other things I could be looking at such as relays etc? thanks in advance

[kvas]

Why do you assume that is suffering from compressor failure if you test it and you see that windings is ok? Sometimes windings are ok but compressor is blocked at the mechanical part.What was the problem before you replace it?

Take a look at this manual and you will find every probably faults on a compressor.
http://www.scribd.com/doc/54217070/SM-Si-53-Service-Check-Points-Compressor

[alan_man]

I didn't have anything to do with the previous diagnosis and unit removal/replace, that was done about a year ago by someone else. The unit I have now was left in storage for the previous year so I decided to pick it up and try find the issue. I understand many tradesman pull the "compressor is broken" line just to get another job out of a customer when the old unit may be suffering from a minor issue. If the compressor is really the issue then no problems, got the unit for nothing

[Tayters]

I am not too familiar with the innards of an inverter model but I have tested the cap as well as compressor windings which seem to be ok.

Hi Alan,

An inverter wont have a start capacitor and the compressor will be a 3 phase star wound type. I suspect you have a single phase motor from your description unless the capacitor was for the fan motor. Easy to check from the wiring diagram on the panel or from the readings you get or a quick butchers at the PCB.

If you have a single phase compressor then all you can do is test windings for resistance, megger them to earth, check capacitor value and operation of any start relay. When meggering you should pump some nitrogen in or at least check the comp isn't in a vacuum or the meggering can cause tracking across the pins internally if you're unlucky then it defintately will be knackered!
Obviously static checks wont confirm a seized unit.

If you have an inverter then there are more checks you can do to prove if the board is good or not to some degree. If that is the case let me know and I'll give you the info.

Cheers,
Andy.