Mitsubishi City multi problems

I have a problem with a m city multi out door unit. I got error 4250 with is a inverter problem.

I tried to run the compressor from an adjacent unit by swapping over the compressor tails. but the compressor wouldn't run. So I suspect the compressor may be knackered. Checked windings - no faults to earth and continuity seems ok..

Output from inverter to netural is around 250v on all 3 legs.

When I spoke to M they advised to change comp & inverter pack!! but inverter pack is £2500.

Any advice how I can test I pack. and will fitting a new compressor to faullty inverter pack damage the compressor?
Any help much appreciated

It is usually fair to say that a faulty compressor can kill a good inverter pack, but not likely that a faulty inverter would damage a good compressor. So if you have tried the supsect compressor on an inverter drive that is known to be healthy, then it is a reasonable assumption that the compressor is no good (probably seized). Although it is possible to test the individual components that make up the inverter drive, you can never be 100% certain that it is ok until you connect it to a good compressor, and put the IPM under load. What you might like to try is running a known good compressor from your suspect inverter pack....HOWEVER proceed with caution as my manager once managed to somehow end up with 2 dead comps and 2 suspect/dead inverters by doing this! Having said that, Mitsu' tech support will usually advise trying the above test.

The bottom line is the only way to give a cast iron guarantee of no recalls is to change the comp & inverter as a pair. If the customer wants to take the chance of changing just the comp first, they should be made fully aware of what could happen. We only ever quote to change the pair.

Always wear baggy pants cooltech1, that is to say, always cover your arse!! :D

cooltech 1
First always check power supply to the unit is good including N to earth to be sure no poor N connection which will cause inverter failure.
Your idea to use nextdoor unit inverter was a risk but did prove compressor was locked.
You must always be absolutly sure that the windings are ok before you do that test because if there is a ground fault you could damage the inverter pack.
Always use a megga test for the windings with leads disconnected. That will effectively test the windings under load. A multi meter ohms test may not show up any ground fault. Note the M ohms lable on the side of the compressor.
So why not use the inverter on your failed unit to run the nextdoor compressor ? You know that compressor is ok. You may need to extend the 3 cables to reach the nextdoor compressor. This will prove 100% your inverter is ok under start up & run under load conditions.
But proceed with this test with extreem caution,monitor the discharge pressure & amps of compressor as it starts & ticks over & then watch carefully when it starts to ramp up. You are running the compressor independantly of the system so all the solenoid valves & lev valves are shut so the compressor is pumping against dead end discharge pipe work so discharge pressure will rise rapidly. You will be the HP switch in this test. So be ready to switch off at the isolator.
The acid test for the inverter is a ballanced supply. Measure each red,white & black power supply cable from the inverter to the compressor to earth,,, it should be within 2 or 3 volts the same. Dont worry to much about the actual voltage as that will depend on your multi meter specification, just that the voltage is the same for all 3.
Some engineers like to also measure between the phases for ballance. You can do that as well but usually I find ballanced phase to earth is enough to prove inverter good or fault.

I carry a small fractional HP 3 phase motor with me & use that to test the inverter. It is very satisfying to see the shaft slowly rotate & then speed up to tick over speed because then you can be 99% sure the inverter is ok. For this test you need to tell the inverter board not to stop on under current amp fault by SW1-1 on.
This test is completely for visual effect & you can do the same without any motor connected but make the red, white & black compressor cables safe in a blank terminal block first.

This stuf can kill you so saftely first !!!

It is much cheaper to rebuild the inverter pack with new components than buy a new or reconditioned one.
But you must know exactly what you are doing other wise you can blow the new components the first time the system starts & you have to explain to the customer & your boss that you made a mistake which has just caused 1k damage ,,, oops.

I looked at a YMF-C last week. Comp windings down to ground. inverter ok with test motor connected.Comp run hours recorded at 47,000 hrs !
Contractor will change out comp this week & has my assurance that the inverter is good.

I would check again with M they have some real good Tech guys and some not so hot, I had a problem with a set the other day and could get no action from the C/U the fault code inicated a failed coms board, or comp stuffed....and low and behold thats just what the first Tech guy said, I checked fuses leads all the basics eventually one very good Tech guy said Ah make sure you power the c/u first then the AHU log and behold off she went good as gold - now most of us are not electronics engineers and have to rely on what info we get which can lead to a bad call but worth a second try ring there Tech ask for Dan he was spot on !

It is easy to check total function of Inverter PCB.
Just connect 3 light bulb or reflectors (try to match their power with compressor motor power) in star.
Here, you got more on that subject:
http://www.refrigeration-engineer.com/forums/showthread.php?p=84657#poststop

Go to the search tab at the top of the screen and type in inverter checker. The first result should be titled "Cheap Inverter Checker".
Have a read through this thread as you will find a lot of usefull information.

Regards

Fatboy

Polestar

It is always a good idea to do a power reset with everything switched off, indoor units B/C box & outdoor unit.If the system will go again then you can carefully monitor the system running to see if there is any problem which might cause the system to stop on the fault.
If its an intermittent fault then it will work again for a while.
But before you do the power reset look to see if the fault history shows multiple stops on the same fault. Then you know if you have an ongoing problem or if it was a one off.
The outdoor unit records the last 10 fault codes & the G50 or MJ103 records 13 pages of fault record with date & time for each fault.

If you re getting 4250 error, replace fan inverter board.- I have experienced such problem.

to check compressor / inverter output power down condenser . Disconnect compressor leads and switch DS1 bit 1 to on . Turn on power and check volts on leads . The inverter power should show a balanced output . If not then an integral part of inverter pack may be faulty .

very good

great