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Tyler Z.
Tyler Z., Appliance Doc
Category: Appliance
Satisfied Customers: 80228
Experience:  9+ years being an appliance technician with factory training.
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I have a Sub Zero 650. A month or two ago I noticed it was

Customer Question

I have a Sub Zero 650. A month or two ago I noticed it was not getting as cold -- around 42 degrees in the refrigerator even when the thermostat was set all the way down to 34 degrees. I noted that it had an error code of 50 (excessive compressor runtime) on the display.

To attempt to resolve, I first I cleaned the condenser up top. Then I opened back panel inside the refrigerator and found that the refrigerator evaporator was frozen (see pic). I defrosted it and the drain line, then put it all back together. For about it month, it was working fine, but now the problem has reoccurred. Popped open the panel and the refrigerator evaporator is all frozen again.

What's going on with this thing? Do I have a refrigerant leak, is the evaporator defroster not working or is a thermistor simply shot? How can I tell? I wondering if it's a simple fix or if I need to call a very expensive Sub Zero repairman.
Submitted: 3 years ago.
Category: Appliance
Expert:  Tyler Z. replied 3 years ago.
Hello, and thank you for using this service. I'll be helping you with your problem today.

I can't see your picture that you said you attached for me to see. Can you please reset the picture? Or upload it to and then give me a link to the picture?
Customer: replied 3 years ago.
Expert:  Tyler Z. replied 3 years ago.
OK can you thaw all the frost out with a hair dryer please and then take a picture a little further away so it's not so zoomed in please?
Customer: replied 3 years ago.

Yikes, I did that earlier. I defrosted it and put it all back together already. Now I'm waiting for the refrigerator to come back down to temp so my food doesn't spoil.


Is there something specific your looking for?

Expert:  Tyler Z. replied 3 years ago.
I'm trying to see if your model even has a defrost system on it. There would be a heater running along the bottom of it if it has a defrost system.

Customer: replied 3 years ago.

You know, now that I think about it, I don't think it does. I don't remember seeing any extra bars or connections reflective of a heater.

Expert:  Tyler Z. replied 3 years ago.
OK well that I what I thought, but you were talking about a heater so I wasn't sure. Either way, this model uses the downtime when the compressor shuts off to melt the frost that forms on the coils since the refrigerator is warmer than the freezer. It's a really touchy system however. If too much frost builds up, it won't melt appropriately and then it won't cool as well causing it to stay on longer and longer. There is a threshold where it gets to the point where it can no longer cool and the problem gets worse much quicker with frost accumulation. Now your thermostat isn't going to be the problem because the refrigerator isn't OVER cooling (freezing) when you thaw all the frost out. That means that either too much moisture is getting into the refrigerator for some reason, or the refrigerator is set too cold, or possibly you have a freon leak (much less likely). You'll want to check both the refrigerator and freezer door seals to make sure they are sealing up properly. If either of them are ripped, you need to replace the door seal. Other than that, turn the refrigerator temperature up a few degrees and hopefully the problem doesn't come back. If it does, you'll need a technician to come out and check the freon pressure.
Tyler Z. and 3 other Appliance Specialists are ready to help you
Expert:  Tyler Z. replied 3 years ago.
I'm just following up to see how your appliance is doing since I haven't heard back from you and this question is still open. Is there anything else that I can help you with today?
Customer: replied 3 years ago.

Sorry I've been out of touch. I noticed that the refrigerator does seem to be overcooling -- It's set to 38 degrees and it has been dropping as low as 30 degrees. This was verified by using two appliance thermometers.


The refrigerators diagnostics seem to indicate a periodic problem with refrigerator thermistor. Does it make sense to replace this in an attempt to resolve this issue?

Expert:  Tyler Z. replied 3 years ago.
Aye, I would replace the refrigerator thermostat. if it's getting too cold sometimes. That would make more sense.