Mitsubishi ASHP fan motor failure (and hopefully repair)

[ProDave]

My plumber up the road called me today.  His Mitsubishi ASHP has stopped working.  Model number PUHZ-W85VHA2

 

Symptoms.  It just does not work.  No errors shown on the in house display panel.

 

Went outside took the cover off the control panel on the outside unit.  Gave it a heat demand and watched.

 

After a short while the compressor started, but the fan motor did not start.  After a minute or so the compressor stopped and the on board 2 digit 7 segment LED display showed the code U8 which means fan failure.

 

The fain looks very similar but not identical to my fan motor in my LG ASHP.  It has an inbuilt variable speed controller.  It is supplied with 320V dc (rectified 230V ac) and has a few low voltage control inputs.  Unlike my motor, it does not identify on the label what wire does what.  So testing today was somewhat limited, other to confirm the 320V dc is pesent.

 

The motor has the part number RG61V143H35 on it.

 

What I have done so far:

 

I have found the service manual, it can be downloaded here https://www.manualslib.com/manual/769585/Mitsubishi-Electric-Puhz-W85vha2.html#manual

 

And the Mitsubishi parts list is here http://www.mitsubishitech.co.uk/Data/Ecodan/Air/Monoblock/Outdoor/PUHZ-W/2012/PUHZ-W85VHA2_SP_OCB465A.pdf

From that I have determined the Mitsubishi part number for this fan motor is S70E10763

 

Next steps:  The service manual tells you how to check the 320V and 15V supplies to the motor, so I will go back and do that.  There are no test points on the control pcb and the connector does not lend itself to meter probes, so I will splice some test points into the motor lead before going back to do more tests.

 

The only 2 fault conditions identified in the service manual are faulty motor - replace (list price about £400) or replace control PCB  (no idea how much that would be)

 

I think the chance of repairing the motor is nill, as far as I can tell all the electronics inside the motor are encapsulated in a plastic moulding.

 

More to come I am sure.....

[ProDave]

I was back today.  I confirmed the 300V dc and 15V dc supplies to the motor are present, and when the compressor starts, the other 2 (exact function not determined) connections have variable voltages present.  One will be the speed demand.

 

So the motor is dead.

 

The list price appears to be just over £400 plus VAT plus postage.  That is a criminally high price in my opinion.  Anyway I found one listed on ebay for £200 so that has been bought an on it's way.

[The Bin Man]

Is an approximate runtime before failure known for the fan motor?

[ProDave]

This ASHP is about 10 years old, well outside guarantee and this is the first time there has been a failure.

[The Bin Man]

It’s done well then.  Hopefully your replacement part does the trick.