Frigidaire Freeder model MFU17M3GW1 has poor cooling, excessive frost

[willie2]

Hello,

 

I have a Frigidaire upright freezer model MFU17M3GW1, serial no. WB94118935 and it is not cooling properly.  The thermostat is set to the coldest setting and there is excessive frost build up on the top shelf and no frost on the lower shelves.  The compressor is running continuously.

The unit has always had more frost on the top shelves vs. the lowers but the lowers always had some frost on them.  I initially thought that someone left the door ajar and that is why the frost built up but after I discovered the lower shelves had no frost on them, I am thinking it may be low on refrigerant.

My first thought was to clean the condenser coil fins but this unit does not have a condenser fin unit like a refrigerator does.  The evaporator is essentially the refrigerant lines attached to the shelves.  I think I need to completely defrost the unit and go from there.  Anything else I should check?

[vee8power]

It does sound like a refrigerant leak or some other sealed system problem. A sealed system is about all there is on this unit.

[willie2]

It was a tad low on refrigerant so I added a slight amount.  The unit began cooling throughout (it was thawing on the lower half) but with the thermostat set to the coldest setting, it only pulls down to 18°.  At the coldest setting, it should be -10°.

I checked the amp draw of the compressor and it was 2.00 amps and the label states 5.00 amps.  The compressor runs continuously and is very warm to the touch.  I believe the valves in the compressor are shot.

It is difficult to find a manual defrost freezer these days.  The frost free units seem to ruin food that is stored any length of time,  I can buy a compressor kit for $145.00 and it is no problem for me to braze it in.  I've looked at several youtube videos on  compressor swaps and none of the guys did a nitrogen purge.  Wouldn't the oxide left over ruin the new compressor?

[Hiroshi]

Yep its a goner, sorry man. Without locating the original leaking point, a compressor may not be the answer... and if there isn't a purge, you would likely have contaminated oil left in the system eating away at the tubing and new compressor... it's just a can of worms.

If you are willing to install a compressor, I would look for an older unit to invest the work in and you will be better off. Find a used one that is like 20 years old (that is still working with no leaks), buy it for a song, and cut-in the new compressor without fear of complications.

[willie2]

The unit in question is 19 years old.  My leak detector will detect a leak as small as 1/4 oz per year on the high setting.  On the high setting, it went off around the brazed joints where the evaporator lines on the shelves join the vertical piping.  It wouldn't sound off on the low setting so my theory was any leak had to be so small that it took 19 years to get down to a point where it affected the performance.

The low side was at 10 psi when I first checked it.  I assumed it to be low on refrigerant so I added a very slight amount to bring it in the 3-5 psi/5" vacuum range but the issue may have been a worn out compressor all along.

Is there a chemical flush process that would be done to remove all the old refrigerant oil?  What about the guys who don't use a nitrogen purge?  Wouldn't that leave crud in the system that would ruin a new compressor?

[Hiroshi]

15 minutes ago, Hiroshi said:

and if there isn't a purge, you would likely have contaminated oil left in the system eating away at the tubing and new compressor

There are flushing products and compressor oils here:  http://ph.parker.com/us/en/refrigerant-chemicals-and-lubricants

 

[willie2]

Further diagnosis indicated there was a restriction in the system - most likely the capillary tube.  That coupled with the compressor that has been running continuously for who knows how long, were the final nails in the coffin.  I purchased a new Frigidaire freezer - pretty much the same model.