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ALONEI
20-05-2008, 10:38 AM
Hi to you all

I am working on a Mitsubishi city multy that has a fault.
The problem is that the comp is start to work on nominal current but there is no movment on the gas gauges.
In my opinion the comp is gone.
Does any one have some expiriance on those inverter comp'?

Thanks
Al

The Viking
20-05-2008, 03:05 PM
There are a lot of controls on those units and without a full understanding of what's going on "behind the scenes", the pressures won't tell you much.

If it's an old R22 machine, then you can try and put 3 phase power straight to the compressor and see what happens with the pressures then. (just remember, if you do that-YOU are the safety devices so keep a close eye on things)

If you give us the model No, I will try and dig out a manual for you.

Good luck,

Thermatech
20-05-2008, 10:16 PM
Try a pump down test to see if the comp is pumping or if refrigerant bypass in system or outdoor unit.

Exact model number will be helpfull for any further advise.

Lowrider
20-05-2008, 10:54 PM
Hi Viking,

Posted an e-mail to you a while back, I have a lot off manuals for ME, but it's large! If you want them I'll put them up somewhere and maybe you can put them on your site!




If you give us the model No, I will try and dig out a manual for you.

Good luck,

ALONEI
20-05-2008, 11:44 PM
Hi again
The model is PUHY-P250YMF-C
The refrigerant is 407c

As I said the compressor is working on full capacity but not pumping.
I am waiting for a service manual from Mitsubishi but have no idea what it contains.

Thank you for helping out

ALONEI
21-05-2008, 09:15 AM
Does the code 4250 tell you guys something?

Thermatech
21-05-2008, 10:28 AM
On the YMF-C models 4250 is compressor overcurrent.

1/ check incomming power supply for ballanced 3 ph at acceptable voltage & no N problems.
2/ do the dip 1 on the inverter board to make it disregard low amps disconnect compressor from inverter.
Run the system & measure for ballanced 3ph output from inverter.
If you have other YMF-C systems on site you can also take out the inverter pack & use it in another unit to prove it works ok at load.
At this point you should know if the inverter is good or not.
3/ Mega test the windings of the comp motor for ground fault.
You cannot start this model comp direct on line as it will pull over 100 start amps.
But if the inverter has been proved to be ok, the comp windings are ok but it wont start or stops on 4250 at start up then you have to assume its locked.
BTW it will try to start 3 times & flag 4250 at 4th failed start.

If the comp will run but does not seem to pump then make sure there are no refrigerant bypass from high to low side in the outdoor unit. Do a pump down test with system in test cool & liquid line service valve shut.
This will show up any bypass in the outdoor unit. Use two sets of gauges on the service valves & unit hp & lp service ports.
If the unit cannot pump down to about 40 psi then you have to conclude the comp is not pumping.
BTW you cannot get lower than 40 psi due to oil return circuit.
The most common comp failure on this model has been bottom bearing failure & that causes the comp to lock or the motor windings to ground.
Its very rare to find one not pumping.
If you can get it running & the bearings are worn you can clearly hear a worrying rumble noise from the bottom of the comp.

ALONEI
21-05-2008, 11:49 AM
Dear Thermatech
Thank you so much for your reply.
It is clearly that the comp is trying to start and what you said on the over current nake sense.(I checked it and it looks like it drwes to much and sound stuck)
After the 3rd attempt it goes to lock up on that code.
At the moment I am waiting for the service book from Mitsubishi.
Is this a normal thing for this unit to start for a few seconds and then stop?(self check??)
What hapens is that the unit starts for 3 seconds and stops.
Then I can hear only the comp try to kick in after a few seconds and the rest is what you said.
I appriciate your answer

Cheers
Al

Thermatech
22-05-2008, 12:34 AM
Yes
The unit will monitor over current at comp start & will stop.
A preliminary fault will be logged in the fault history memory & the unit will go for restart following comp restart delay time out.
The unit will try to start the comp 3 times. If it is unable to start the comp after 3 failed attempts due to over current then it will flag up 4250 fault & lock out.
If the unit is unable to start the comp when the power supply is good & inverter power supply to the comp is good then the comp must be locked.

In this case suggest replace comp.
But make sure
Lots of engineers change out the comp only to find that there was also a problem with the inverter or a refrigeration flow problem which caused the premature failure of the comp.

ALONEI
22-05-2008, 12:52 AM
Thanks mate.
Once Ill change the comp I will do all the checks.
Thanks again

philjd26
26-05-2008, 12:09 AM
hi

a thing to watch out for on these units is on start up if the compressor shell is not at a certain temp it will send two phases to the compressor windings inturn raising temp...however the compressor does not pump giving you the impression that its gone...check the temp/resistance of the shell thermistor to see if its ok...

rgrds phil

Thermatech
26-05-2008, 03:45 PM
hi

a thing to watch out for on these units is on start up if the compressor shell is not at a certain temp it will send two phases to the compressor windings inturn raising temp...however the compressor does not pump giving you the impression that its gone...check the temp/resistance of the shell thermistor to see if its ok...

rgrds phil

Good point
These City Multi units go into compressor warm up mode when you
1/ turn on 3 ph power & 2/ the outside ambient temp is less than +5 deg C at Th6 temp sensor.

I know it can get a bit chilly in Melbourn this time of year but possibly not that cold.

In this case you just need to hold TH6 sensor in your hand for a few moments & the outdoor unit then get higher than 5 deg C data & compressor warm up mode is canceled & the compressor will start & run normally.
You can always do the SW1 dips to make outdoor unit display live TH6 data so that you know its getting correct data from TH6.

ALONEI
28-05-2008, 11:40 PM
Thanks guys
I am in the middle of a "fight" with Mitsubishi Australia regarding the service book
They sent me the book for the YMF-B series
While I need the YMF-C series
They insist thats the right book but for instance the code 4250 does not exist there

Thermatech
31-05-2008, 12:40 AM
YMF-C service handbook
page 129
4250 IPM alarm overcurrent

This is the most common fault code for a YMF-C unit with overcurrent fault.

On the older YMF-B model 4210 was the most common overcurrent fault.

Some City Multi history as follows.
PUHY 250 YMF-B was a complete redesign of the old 4 fan unit but still using R22. This was the first unit to have a single condenser fan.
PUHY P250 YMF-B was the same unit but with R407c.
PUHY P250 YMF-C was the next development fully optamised for R407c.
This was the first unit to have 4250 overcurent fault.

All fault codes starting with 42?? are related to compressor / inverter problems.

In the UK we were installing these units in 1998 & 1999.
Very few Mitsubishi employed technical support staff have ever worked on, or even seen kit that old.
If you start talking to young people today about kit that was made in 1998 you just get a blank face expression & you instantly are disregarded as an old timer who needs to be put to rest in an old peoples home.

ALONEI
31-05-2008, 09:25 AM
THERMATECH
Your knoladge on those units are impresive (:
This unit I am working on is from 2001
The guy from Mitsubishi insist that the book about the B model is for the C as well
I am still trying to get the right ont

Thermatech
31-05-2008, 04:56 PM
To be fare the B & C models are almost identical.
The B model still had 100% outdoor coil refrigerant flow & had overcondensing problems in low ambient conditions.
The Y model had big improvement on hp control by additional solenoid valves to make two 50% outdoor coils so that in low load or low ambient conditions the unit could shut down refrigerant flow through only 1 of the 2 outdoor coils.

So although 99% of the B service manual is good for the Y models there are some important differences.

At the end of the day you have a compressor / inverter which is faulting on overcurrent & you need to find out why.
Is the compressor duff or is the inverter at fault or both ?

ALONEI
02-06-2008, 11:25 AM
UPDATE
----------
I have change the compressor today and its working OK
I just need to add a bit more of refrigerant and thats it(I hope)(:

I want to thank you all for your help and tips
Cheers
Al

Refrigerologist
11-01-2009, 04:19 PM
Hi to you all

I am working on a Mitsubishi city multy that has a fault.
The problem is that the comp is start to work on nominal current but there is no movment on the gas gauges.
In my opinion the comp is gone.
Does any one have some expiriance on those inverter comp'?

Thanks
Al

Ignore post as I see you have fixed the problem!