Mitsubishi PUHY250YMF Inverter Problem

[Refrigerologist]

I am having trouble with the inverter on an R22 unit circa 2001. We have replaced a faulty compressor (earth fault) and tested the inverter. The phases to the compressor are unbalanced. I have tried following the Mitsubishi service manual in regard to testing the transistor modules and the diode stack etc. My Fluke multi meter (digital of course) does not appear to be of any use in carrying out the tests. I have tried it on a brand new transistor module and diode pack, but the readings are totally at odds with those sugested by Mitsy. Would I be better off with Metrix MX2 or MX1 analogue meter as these appear to have the single 1.5v cell that Mitsy recommend?

I know we can install a new inverter box at £2,500.00 but this seems a bit excessive.

Now I know why I prefer Daikin. The manuals are so much clearer!

[Thermatech]

The components like diode stack & TRM units & inverter circuit are very similar for Daikin units from the late 1990's they are just packaged up into a box on City Multi units instead of spread out in a large panel on Daikin VRV units.

You will get better results with a £10.00 analog meter from ebay when testing this type of component & should be at least close to service manual data.

But you can also get very good results using a standard mulimeter set to diode mode so long as you know how to do it.(different procedure from service manual )

If you want to do a fail safe inverter recon then replace the TRm's, diode stack, inverter board & contactor.

Capacitors & resistors are easy to test but very rare to fail.

As the comp was down to ground you will have damage to at least one TRM so as precaution best to replace all 3.
Good practice to always replace contactor anyway.
Diode stack not very expensive component so why no replace as precaution ?
That just leaves the inverter board. Not so easy to test but is more expensive to replace.
Mitsubishi recomend always replace it if a TRM has failed as a fail safe procedure. But the inverter board does not always fail with a comp ground fault, so try the old one after you replaced other components & see if you have ballanced supply with comp disconnected. If supply ballanced inveter board is ok , if not ballance then replace inverter board.

After you have rebuilt a few inverter packs you find its actually not so difficult after all & more cost effective than new inverter pack.

The TRM units can be a problem as no one seems to manufacture them any more so some times they are hard to get hold of.

[Refrigerologist]

The components like diode stack & TRM units & inverter circuit are very similar for Daikin units from the late 1990's they are just packaged up into a box on City Multi units instead of spread out in a large panel on Daikin VRV units.

You will get better results with a £10.00 analog meter from ebay when testing this type of component & should be at least close to service manual data.

But you can also get very good results using a standard mulimeter set to diode mode so long as you know how to do it.(different procedure from service manual )

If you want to do a fail safe inverter recon then replace the TRm's, diode stack, inverter board & contactor.

Capacitors & resistors are easy to test but very rare to fail.

As the comp was down to ground you will have damage to at least one TRM so as precaution best to replace all 3.
Good practice to always replace contactor anyway.
Diode stack not very expensive component so why no replace as precaution ?
That just leaves the inverter board. Not so easy to test but is more expensive to replace.
Mitsubishi recomend always replace it if a TRM has failed as a fail safe procedure. But the inverter board does not always fail with a comp ground fault, so try the old one after you replaced other components & see if you have ballanced supply with comp disconnected. If supply ballanced inveter board is ok , if not ballance then replace inverter board.

After you have rebuilt a few inverter packs you find its actually not so difficult after all & more cost effective than new inverter pack.

The TRM units can be a problem as no one seems to manufacture them any more so some times they are hard to get hold of.

Thanks for the info' It seems I am on the right track. I did order one TRM (I thought I was ordering 3) I changed out the worst one plus the diode stack but same problem occurred. So I will just re-order the parts and hopefully it will cure the problem.

[Thermatech]

If you dont get a ballanced output from the inverter but you have replaced the diode stack we can be sure there is good high voltage d/c on the buss bars at the TRM's but they are not switching in correct sequence.

In this case the possibilities are

1/ One or more TRM's have a fault.
2/ The inverter board is damaged & not sending the correct firing signal on the gate leads to the TRM's.
3/ The gate leads have been incorrectly connected.

The fail safe method is to replace all 3 TRM's.
However sometimes only one or two have actually failed caused by the compressor motor ground fault.
So if you can test the TRM circuits correctly then you will know which ones are ok & which have failed & save cost by replacing only the failed ones.

With the inverter base amp board if its damaged you can sometimes see burnt components on the board in the 6 transistor driver circuits.
Measure the resistance at the gate outputs pins is not always conclusive but sometimes gives a clear fail result.

If you are happly with all other components in the circuit like capacitors, resistors, contactor, diode stack & TRM's then you can carry out a live test of the inverter pack using the old inverter board.
But only do this test with the compressor disconneted.
I use a tiny fractional hp motor connected instead of the compressor. Then you can see the motor spin up to the correct rpm & you can measure the inverter output for correct ballanced supply. Most often the little motor will not run if the power supply from the inverter is not ballanced.
In this case you have to suspect the inverter base amp board is damaged & so replace it with a new one.
Only reconnect the new compressor to the inverter pack when you are sure it is supplying a good ballaced 3 phase supply.

[Refrigerologist]

If you dont get a ballanced output from the inverter but you have replaced the diode stack we can be sure there is good high voltage d/c on the buss bars at the TRM's but they are not switching in correct sequence.

In this case the possibilities are

1/ One or more TRM's have a fault.
2/ The inverter board is damaged & not sending the correct firing signal on the gate leads to the TRM's.
3/ The gate leads have been incorrectly connected.

The fail safe method is to replace all 3 TRM's.
However sometimes only one or two have actually failed caused by the compressor motor ground fault.
So if you can test the TRM circuits correctly then you will know which ones are ok & which have failed & save cost by replacing only the failed ones.

With the inverter base amp board if its damaged you can sometimes see burnt components on the board in the 6 transistor driver circuits.
Measure the resistance at the gate outputs pins is not always conclusive but sometimes gives a clear fail result.

If you are happly with all other components in the circuit like capacitors, resistors, contactor, diode stack & TRM's then you can carry out a live test of the inverter pack using the old inverter board.
But only do this test with the compressor disconneted.
I use a tiny fractional hp motor connected instead of the compressor. Then you can see the motor spin up to the correct rpm & you can measure the inverter output for correct ballanced supply. Most often the little motor will not run if the power supply from the inverter is not ballanced.
In this case you have to suspect the inverter base amp board is damaged & so replace it with a new one.
Only reconnect the new compressor to the inverter pack when you are sure it is supplying a good ballaced 3 phase supply.

Thanks again! I know the inverter output is unbalanced as one phase is higher by 12 volts to neutral with the compressor windings disconnected. I definitely had at least one faulty TRM as one was completely at odds with the other two. Unfortunately none of them, including the new one, can be tested properly using a digtal meter. I have ordered a cheap analogue meter so that I can test them in accordance with the manual. The old diode stack checks out as ok using the diode test on the Fluke meter. As for the gate leads these are connected correctly, I have checked these against the drawing and the cable colours are correct as per drawing. It may be that the board is cream crackered, but there are no visible signs of any blown components. I'll let you know how I get on.

[Refrigerologist]

Hi guys, I thought I had better update you on this problem.

Eventually replaced the entire inverter board again, phases balanced at 273volts to neutral, but compressor failing to wind up above 40hz. We suspected a tight compressor, Mitsubishi Tech were unable to offer any solutions.

Andy from Mitsi paid us a visit! He disconnected the compressor current sensor, and via the laptop, wound the compressor speed manually. The compressor worked fine and pulled about 6amps. Left it running for about 2 hours, then reinstated normal control with the current sensor in place. The compressor pulled about 13amps max, so seems ok.

The compressor now occassionally trips on overcurrent, usually after a weekend. Mitsubishi will be supplying a new inverter board with a slightly higher current tolerance. Apparently the TRM's are now manufactured a different company and the resistances have changed. This can cause a problem with some compressors!

[Thermatech]

I have got the same problem on two other sites with YMF systems.

Contractor has installed new compressor & new inverter pack complete but now units intermittently trip on 4210 overcurrent.

Some components in the new replacement inverter packs are different.

The current sensor on the older CM units was on the high votage d/c bus bar.
But the compressor does not pull excessive amps when monitoring the incoming 3ph power.

Reprograming the inverter board for slightly higher trip current on the d/c bus would be a good counter measure.

Let us know if it works as I have two customers who are fedup with intermittent 4210 overcurrent faults.

[Brian_UK]

Thanks for the update.

[Refrigerologist]

I have got the same problem on two other sites with YMF systems.

Contractor has installed new compressor & new inverter pack complete but now units intermittently trip on 4210 overcurrent.

Some components in the new replacement inverter packs are different.

The current sensor on the older CM units was on the high votage d/c bus bar.
But the compressor does not pull excessive amps when monitoring the incoming 3ph power.

Reprograming the inverter board for slightly higher trip current on the d/c bus would be a good counter measure.

Let us know if it works as I have two customers who are fedup with intermittent 4210 overcurrent faults.

We installed a new inverter control board on Thursday. Same problem only worse, now it trips on 4210 overcurrent fault more frequently.

I checked the inrush current with the current sensor disconnected, the whole unit pulls 7.4 amps on compressor start up, then drops to 5.4 amps before winding up to higher speeds. At no time did the current draw rise above 14amps.

I am awaiting an answer from Mitsubishi Tech who are awaiting an answer from the factory.

I'll keep you posted!

[icecube51]

this same stuff cost me a compressor i had instaled and only runs 2 weeks. then one fault after an other apear. even had 85Hz and 132C° head temp. they are going to look for explanation as well.

Ice

[icecube51]

you need a multi tester whit RMS capabillity,see if the incomming current is in balance before you test the inverter balance. and do so whit the compressor wiring disconnected.

beware this units have a HP sensor and no LP sensor. and don't thrust the A.L (accumulator level) code, use your gauges on both side's high and low presure.

Ice

[Refrigerologist]

you need a multi tester whit RMS capabillity,see if the incomming current is in balance before you test the inverter balance. and do so whit the compressor wiring disconnected.

beware this units have a HP sensor and no LP sensor. and don't thrust the A.L (accumulator level) code, use your gauges on both side's high and low presure.

Ice

We have already established the inverter is providing a balanced output. This has been tested by me and the Mitsubishi tech who attended site, (pre christmas). He obtained a new a new modified inverter control board for us to install. This is a modified board that supposedly uprates the current sensor read back circuit in order to prevent unnecessary tripping on overcurrent.

We installed the new board, but unfortunately the fault is still present. The equipment sometimes oeprates for a couple of days with no problem and then fails on overcurrent 4210 for no apprarent reason. All checks, and there have been many, show the compressor start and operating current to be normal.

The Mitsubishi Tech returned to site a couple of days ago to ensure that the new board had the correct modification, which it does, he is awaiting a response from the factory!

He has told me again that the TRMs' on the new inverters are the cause of the problem and that the modified board normally cures the problem. However he has said it may be necessary to replace the compressor again with one of a different type with a lower operating current characteristic! Obviously having already replace a faulty compressor this is the last thing we want to do!

[Thermatech]

Same as that.

On one site we are at the stage of testing the old Fuji TRM units & the new Mitsubishi TRM units.

As you have advised the new replacement Mitsubishi TRM units have slightly differerent resistance readings on the gates & switching circuits. They seem to draw more amps at start up.

So is the problem with the new TRM units which draw more amps or with the inverter circuit board which trips on high amps although nothing wrong with the compressor ?

We have already proved no problem with the compressor as we have fitted the new inverter pack to another system which has the same compressor model but has no history of 4210 faults & the compressor runs perfect no problem & the fault has gone with the inverter pack, which still trips every day on 4210.

ME used Fuji TRM components for many years but in time they became obsolete & the supply of these components dried up.

ME had to make alternative arrangements for the supply of this component.

The test we are carrying out at the moment is new inverter pack which was tripping every day on 4210.
but
we have fitted old second hand Fuji TRM's.

Soon we will see if the problem is with the TRM's or the inverter board.
Will advise when we get conclusive result.

BTW
Hidden agenda = make problems with supply of spare parts so that contractors & endusers will buy new R410a systems.

[nike123]

What is TRM?

[Thermatech]

Transistor Relay Module
or
Power Transistor Module

Before IPM inverter component which is one unit manufacturers used three TRMs to switch DC to make 3 ph to compressor. One TRM for each ph.
All three connected together with + & - busbars.

TRMs are now old obsolete technology as everyone moved on to IPM components.

[nike123]

Transistor Relay Module
or
Power Transistor Module

OK, from Fujitsu literature it is known to me as Power Transistor Module!

[Mozambezi]

I had same problem, but in this case packed up 6 months old R unit. After board replacement been done and thoughts about Japanese quality I've checked charge and EV work on commisioning and came up with wrong charge and presets on dip switches.

[Refrigerologist]

Same as that.

On one site we are at the stage of testing the old Fuji TRM units & the new Mitsubishi TRM units.

As you have advised the new replacement Mitsubishi TRM units have slightly differerent resistance readings on the gates & switching circuits. They seem to draw more amps at start up.

So is the problem with the new TRM units which draw more amps or with the inverter circuit board which trips on high amps although nothing wrong with the compressor ?

We have already proved no problem with the compressor as we have fitted the new inverter pack to another system which has the same compressor model but has no history of 4210 faults & the compressor runs perfect no problem & the fault has gone with the inverter pack, which still trips every day on 4210.

ME used Fuji TRM components for many years but in time they became obsolete & the supply of these components dried up.

ME had to make alternative arrangements for the supply of this component.

The test we are carrying out at the moment is new inverter pack which was tripping every day on 4210.
but
we have fitted old second hand Fuji TRM's.

Soon we will see if the problem is with the TRM's or the inverter board.
Will advise when we get conclusive result.

BTW
Hidden agenda = make problems with supply of spare parts so that contractors & endusers will buy new R410a systems.

Your conclusions confirm our own, maybe I will test a few second hand TRM's and see if we can find three that are good and then fit these.

I'll let you know how we get on with Mitsubishi tech, on whom we are awaiting a response!

[Refrigerologist]

Another update:

Mitsubishi asked us to swap the inverters from the faulty PUHY 250 with a Pury 250 on the same site.

We had to swap the the front boards back as they are of course, completely different.

And guess what, both systems are now working correctly! No faults whatsoever. Both have been operating for 5 days.

I am awaiting Mitsubishi's response as I do not feel this is a satisfactory solution, after all we now have a new compressor being controlled by a 9 year old inverter!

[Thermatech]

Is the compressor the same model on both systems ?
One is a new replacement compressor but is it the same model as the old original one ?

one system is PUHY YMF
the other is PURY YMF

both systems use the same compressor & inverter pack when new.

So why would the system with a new replacement compressor run fault free with an old inverter pack but continually fault with the new inverter pack connected ?

Does the old inverter pack have FUJI TRM's ?

We have been running a system with new inverter pack which was stopping every day on 4210 before but now have installed old second hand Fuji TRM's & its not stoped on any fault for 3 weeks.
We also have a PURY YMF system with new replacement compressor which was tripping every day on 4210 when a new replacement inverter pack was fitted
but now with an old original inverter pack fitted has been operating fault free since December.

So the old Fuji TRM's work ok on old original compressor & new replacement compressor
but
new Mitsubishi TRM replacement part will not run with new replacement part compressor & will run ok with old original compressor.

BTW
I have been many times to Jersey working on City Multi kit but the only site visit I ever did on Gernsey was at a radio station in October 2002 that was some CM units in a computer room I seem to recall.
Do you by chance look after that site ?

[Refrigerologist]

Is the compressor the same model on both systems ?
One is a new replacement compressor but is it the same model as the old original one ?

one system is PUHY YMF
the other is PURY YMF

both systems use the same compressor & inverter pack when new.

So why would the system with a new replacement compressor run fault free with an old inverter pack but continually fault with the new inverter pack connected ?

Does the old inverter pack have FUJI TRM's ?

We have been running a system with new inverter pack which was stopping every day on 4210 before but now have installed old second hand Fuji TRM's & its not stoped on any fault for 3 weeks.
We also have a PURY YMF system with new replacement compressor which was tripping every day on 4210 when a new replacement inverter pack was fitted
but now with an old original inverter pack fitted has been operating fault free since December.

So the old Fuji TRM's work ok on old original compressor & new replacement compressor
but
new Mitsubishi TRM replacement part will not run with new replacement part compressor & will run ok with old original compressor.

BTW
I have been many times to Jersey working on City Multi kit but the only site visit I ever did on Gernsey was at a radio station in October 2002 that was some CM units in a computer room I seem to recall.
Do you by chance look after that site ?

Is the correct answer! I have no idea why the swapped inverters would work correctly, as you say the compressors are identical.

Only Mitsubishi are likely to be able to provide an answer!

No I don't look after that particular site.

[K.R.Iyer]

Thermatech & Refrigerologist,

I have handled only chillers and not familiar with inverters. Like everywhere else, in India also Inverters are becoming popular and Mitsubishi has entered India recently. The electronics in Inverters really scares me - as I am not an elctrical engineer. But I may not have much choice in the future. YOu guys seem to handle it so comfortably. Could you give me some site / link refrence to understand the basics of inverters control panel function - ofcourse in simplified language for non-electronic guys to understand. Thanks!

[Thermatech]

K.R.Iyer

I do uderstand your possition
I was the same about 15 years ago

The most I was learning was one day with independant industrial inverter repair agent engineer at his workshop.
Later I did have some inverter training from inverter design engineer at Japan factory which was very helpfull.

But otherwise reading service manuals & testing failed components & new components to see what works & what goes bang.

Only joke

All inverter circuits work in similar way so once you understand that you can trouble shoot most failure problems & make repair.

Mitsubishi supplier should be able to provide you with any technical support & inverter diagnostic training.

[K.R.Iyer]

Thanks for the encouraging words Thermatech! From this thread, I have picked few terms like TRM, 4210.

[laf100]

My 2 penneth- I have a site with intermittant 4210's on a Pury 250 ymf-A that has also had a new comp and complete invetrer drive "pack". Apparantly the un-official solution is to fit a ymf-B compressor (as told to me by Mitsu' engineer/instructor)!! Luckily my end user is happy to live with the 4210's as they are only about once a week at most.

[Refrigerologist]

My 2 penneth- I have a site with intermittant 4210's on a Pury 250 ymf-A that has also had a new comp and complete invetrer drive "pack". Apparantly the un-official solution is to fit a ymf-B compressor (as told to me by Mitsu' engineer/instructor)!! Luckily my end user is happy to live with the 4210's as they are only about once a week at most.

That is exactly what I have been told, a different compressor is the usual fix not exactly what we want to hear, but it does seem to be Mitsi' solution. AND the PURY 250 , which now has this inverter pack installed into it, is now tripping occassionally on 4210.

Looks like a reclaim of gas and the replacement of a perfectly good compressor. From whom should I reclaim my expenses?