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Phil
Phil, Shop owner
Category: Appliance
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Experience:  Degree, Mech. engr. shop owner. 51 years experience
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I have a ColdTech commercial refrigerator model #J1GR-24L

Customer Question

I have a ColdTech commercial refrigerator model #J1GR-24L that is suddenly running constantly and does not turn off automatically. Is freezing the contents of the unit. Even turning the thermostat to the off position does not turn the unit off - it continues to cool.
Submitted: 1 year ago.
Category: Appliance
Expert:  Phil replied 1 year ago.

Hello, the manual does not provide us with a wiring diagram for trouble shooting the unit.

It is most likely a bad thermostat or bad printed circuit board or one of the attached temperature sensor thermistors that is causing the problem.

Tell me a lot about your technical background so that I will know best how to coach you...I will also need to know which direction you are from the center of the nearest city.

If you can take a photo of the wiring diagram glued to the back of the refrigerator or on the inside of the compressor service access panel that will help immensely.

You can attach the photo using the paper clip icon at the right end of the tool bar above.

it needs to be upclose, and well focused.

We can go from there.

Customer: replied 1 year ago.
Thanks for the prompt response. Have attached a picture of the wiring diagram per your request.BTW - the upload is now an "+ Add files" link to the left of the send button.My first suspect was the thermostat as well - especially since the compressor did not shut down when I turned it to the off position. When I pulled the thermostat and checked for continuity it seemed to work ok - when in off position there was no continuity and when on I had continuity.Guess I would say I have above average technical skills - worked for a while in college as an electrician and installing burglar alarms. Have also done a fair amount of car repair/restoration.Thanks,
Rolland
Expert:  Phil replied 1 year ago.

Hello again, thanks for all that, especially the clue about the +add files button to the left of the send button. I will give those instructions a try.

The wiring diagram shows no printed circuit card or electronics, just that thermostat as the only control in the circuit. Tell me if the compressor runs with one of the wires removed from the thermostat.

If the compressor still runs that would be truly amazing since the only power source to the compressor is through the thermostat. I suspect the contacts in the thermostat are burnt and under power arc across sufficiently to power the compressors (that would be unusual) but possible.

If the removing one wire from the thermostat stops the compressor, replace the thermostat, there is a 99% chance that will work... there is a 1% chance that there is a short in the terminal block shorting as shown in my red mark up at the link below

http://screencast.com/t/vBCrYxnWCvu

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http://pacificcontrols.itrademarket.com/828414/p-f-n-controller-for-low-temperature.htm

Tell me if that looks like what you have or not, we can go from here without a time limit.

Customer: replied 1 year ago.
Okay - you are correct (no surprise there) - the compressor did not turn on with one wire disconnected from the thermostat. The circulating fan (evaporator fan) did turn on and stayed on - I may have mislead you previously, what I noticed was the fan not turning off - the compressor may have turned off initially and I was just looking/listening to the wrong thing. Is it okay that the fan stay on?Took it one more level and reattached both wires to the thermostat - turning the thermostat off and on definitely cycled the compressor (listening to the right thing this time). Evaporator fan did not turn off - ran in both the off and on positions.Given the above it you are still thinking the thermostat is the problem (i.e. it dd not heat up in my quick test and fails when under a load for a while). If so then it is easy enough to replace. Found one online at Heritage Parts for $37 - is that a reasonable price and vendor? Is there anything else that could cause the same problem I should check?https://www.heritageparts.com/Manufacturers/Metalfrio/METALFRIO-THERMOSTAT/p/MTO%252FPFN-250C-01#Thanks
Expert:  Phil replied 1 year ago.

Hello again, the inside fan runs all of the time. The thermostat is designed not to let the compressor come on again after the box cools off until its sensor is above 35F at which point any ice on the cooling coil has melted.

$37 is a reasonable price.

However if you have not cleaned the condenser coil (radiator with the fan near the compressor) the compressor will over heat and go off on its heat sensitive over load.

Look all that over, clean as needed, then tell me how well the box holds the set temperature.

We can go from there.

.............

I work here on my own time and expense, and am only paid if you ratemy work.

Please remember to rate my service before you leave today. It is how I earn a living, and does not increase your charges.

If you need anything else, just let me know. You can continue asking follow-up questions at no additional cost.

Customer: replied 1 year ago.
Following up - blew out the condenser coils with compressed air, cleaned the fan and reassembled. Has held a constant temp of 38 deg F for the last 48 hrs . . . coils were not all that bad but were a bit dusty - could that have been my only problem?
Expert:  Phil replied 1 year ago.

Hello again, the only thing that would cause the contents of the refrigerator to freeze at the lowest thermostat lettings is burnt contacts inside the thermostat.... you have simply messed with it enough that contacts came unstuck.... the odds are in the 95% range they are burnt and will stick again.

It will be a good idea to replace the thermostat.

.........

Please remember to rate my service before you leave today. It is how I earn a living, and does not increase your charges.

If you need anything else, just let me know. You can continue asking follow-up questions at no additional cost.

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