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John
John, restaurant equipment technician
Category: Appliance
Satisfied Customers: 2136
Experience:  25+ years experience. I'm now employed by a commercial cooking equipment service company
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I have a 427r. last week, the unit out if nowhere has the

Customer Question

I have a 427r. For the last week, the unit out if nowhere has the temperature in both the top and bottom start creeping up. Fan is blowing but not cold. I shut the unit off and then back on at the breaker and then it works fine again...a day or 2 later...same problem, same solution. Any ideas?
Submitted: 1 year ago.
Category: Appliance
Expert:  John replied 1 year ago.

The first thing to do is inspect the condenser coil to see if there is a layer of dust blocking the air flow through it. If there is, vacuum it with a ShopVac to remove it.

If this doesn't restore proper cooling, please get back to me. Thank you.

Customer: replied 1 year ago.
Thanks John. Already have done that.
Expert:  John replied 1 year ago.

OK. Thank you. I'll look further for parts information, and I'll get back to you.

Expert:  John replied 1 year ago.

Your cooling system control board uses a heat sensing thermistor to determine the cooling set point. Its part number is(###) ###-#### If you call guaranteed parts, inc. at 1-***-***-****, you can order the part. There is a thermistor for each section. If you need an owners manual, type the words "sub zero 427r manual" into your Google search box, and choose from the websites offered there. If you need more help, please get back to me. Thank you for choosing JustAnswer.

Customer: replied 1 year ago.
Thanks John. Why would switching the unit off and back on at the breaker fix the problem temporarily?
Expert:  John replied 1 year ago.

The control board tends to erase the voltage values in it, when the power is removed. Since thermistors are voltage producing devices, it takes a bit of time for the board to determine that there's a problem with the signal it's receiving.

Customer: replied 1 year ago.
Thanks again John. The same issue happens at the same time on both top top unit (wine fridge) and bottom fridge drawers. Is this one part you mention above (thermistor) that controls both?
Expert:  John replied 1 year ago.

There is one for each section.

Customer: replied 1 year ago.
Wouldn't it be unlikely they both went bad at same time? To help, the control board was replaced back in November. Issue above only started several weeks ago. Not sure if they could be related
Expert:  John replied 1 year ago.

Before we go any further on thermistors, I want you to use a piece of note paper, or a paper bill, and insert it in several places around the door seal gaskets. When the door is closed, check to see if there is resistance to pulling the paper out. If you find spots where there's little or no resistance, you'll need to replace the gaskets. Please let me know what you find with this seal test. Thank you.

Customer: replied 1 year ago.
Thanks John. Let me give that a shot tonight and get back to you.
Expert:  John replied 1 year ago.

OK.Thank you.

Customer: replied 1 year ago.
John. Thinking more thru this. Unit runs on two separate compressors right? If the gasket is bad, it would have to be bad on both top and bottom. Unlikely. The problem occurred several weeks ago for first time and is impacting both the top and bottom parts of the unit in the same way. Am thinking has to be related to the new control board installed end of last year?
Expert:  John replied 1 year ago.

Yes. I think you're correct. The control board package part number is(###) ###-#### ***** it's available at www.certifiedapplianceparts.com. Door gaskets tend to deteriorate at the same rate, and it's a good idea to replace both, if one is obviously leaking.

Customer: replied 1 year ago.
Another question John. Could it be the relay on the compressor? Do these units have 1 or 2 compressors and relays?:
Expert:  John replied 1 year ago.

I'm sorry I didn't answer your question in my last response. There is a separate sealed refrigeration system for each section. The compressor relays are electromechanical, and very reliable. They rarely fail, and when they do the compressor won't start.

Customer: replied 1 year ago.
Got it. Thanks John. And 1 control board for the entire unit? In which case, must be the control board.
Expert:  John replied 1 year ago.

That's correct.

Expert:  John replied 12 months ago.

Do you need any more help, before your request times out?