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501F Sub Zero Freezer sealed unit repeat repairs


Premium Member
Mar 5, 2020
Model Number
More than 10 years
We have a pair of subzero 501 built in refrigerator and freezers. Even though they are from 1987, the appliance repair professional we initially had come look at another appliance had from the beginning said that he would never replace them. Any part that needed work he could get.

We initially had him come back to look at the refrigerator side. The refrigerator was having by freezing and condensation problems and the hose to the drip pan was clogged. This was fixed by adding a second thermometer to balance the interior temperatures and replacing one of the heater units underneath to keep the hose to the drip pan from freezing.

At the same time we asked why our freezer was forming ice in the bottom (but otherwise working as it should). The answer was that both defrost heaters had stopped working. Those were replaced and the unit started working as it should.

Until it didn’t. Repeatedly.

A few weeks later we noticed the freezer temperature increasing rapidly. He was back out that night and replaced the compressor switch assuming it had been ready to break, and just happened to happen then. A month later we returned home from vacation to a room temperature freezer with rotting food. The diagnosis was the compressor had failed and it was replaced. Since we were offered a deal, we decided to go ahead with the ice maker install that we had wanted for some time. While he was back two weeks later to install he noticed it still wasn’t getting down below 7 or 8 degrees. He balanced the refrigerant levels and replaced the switches on the door having determined that they weren’t functioning and the fan was not turning on.

Now a month after this the we noticed our food was starting to thaw. We checked the temperature and it was only maintaining refrigerator temperatures. It stayed at 40 all evening. This morning it was 50 and climbing fast. When it was starting to heat the interior and was reaching 80 I turned it off. So what gives? We’ve touched basically every major component of this unit and it’s still having problems. We are call8ng in another repair this morning but I wanted to see if anyone else had any thoughts.

We don't get into sealed system repairs here because they can become very complex to do and requires special equipment which normal consumers do not have.

Basically all I can ask you is what the tech. did when he/she replaced the compressor.

Did the tech replace the filter drier when he/she replaced the compressor?

Whenever you open up a sealed system to do any repairs you MUST always replace the filter drier, then use a vacuum pump to evacuate the sealed system to remove all the all the AIR from the sealed system lines, then charge it with refrigerant.


Thank you for your initial response. I'm definitely not looking to DIY this, but the forum didn't have any other clear place to ask this question. More than anything I am looking for what questions I should be asking. Are you suggesting this is most likely an issue with the sealed system again? Without opening the bottom compartment, I believe the fan must have still been running because I could feel warm air being blown inside the unit (and this was with the door open) right before I shut it off. It also generally sounded like it normally does. The evening before when it was maintaining refrigerator temperatures it was exhausting cool air through the toe kick grille when this is usually warm.

I would have to look at the invoice to see if it gives detail or ask the question regarding the filter drier (what is this?), nor do I remember specifically if a vacuum pump was used. I guess I didn't ask a lot of questions and tried to stay out of the way last month. I do remember that he came with a full cart of equipment and couple cylinder canisters, and the full process took about 4 hours and included rechecking all of the levels and confirming that the internal temperature was starting to go down. Does that help at all?

Also thank you for fixing my generic topic title and inverted model number, if that was you, or whoever helped me with that.
Here's a normal filter drier:


The old filter drier has to be welded off, and the new one welded back in its place.

The warm air comes from the condenser and compressor, which is on the outside of the unit.

Yes, it does help to see he came with a full cart of equipment and couple cylinder canisters, I'm sure he knew what he was doing.

Its best to have him come back to see what's going on.

Back in 1987 they used R12, which is now banned.

It's complicated, but in a nut shell, If you can find an R12 replacement compressor you can use R134a refrigerant. You can't use an R134a compressor in an R12 system. The main reason is the compressor oil. R134a compressors use an ester oil. Ester oil can't tolerate any trace amounts of chlorine based refrigerants. R12 replacement compressors use alkyl-benzene oil. It doesn't have the extreme hygroscopic tendencies of ester oil. When replacing R12 with R134a, special care is required. Such as two sets of refrigerant gauges (one for R12 one for R134a) and a sweep charge and purge by heating the evaporator for 10 minutes.


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