# Help diagnosing sub-zero freezer issue



## harryc (Mar 13, 2012)

Good afternoon. Everyone!
I have a sub-zero model 511 from the early 90s. Although it is older every mechanical part has been changed to newer equipment. Recently I just had the refrigerator compressor, heat exchanger, coils, thermostat, and other parts replaced to the tune of $1400. A few years ago I also had replaced the freezers compressor. Pretty much the entire appliance is new except for the cabinet. 
Ever since I owned this beast I have noticed that the freezer never really gets cold enough. I have put a thermometer in it and it basically will not get below 10 degrees F. This is with the thermostat set all the way to 10!
When I told the service tech this he changed the thermostat for me since he had the whole thing apart anyway. This did not fix the issue. 
Last year I had changed the defrost timer because the older one froze up. 
The service tech told me that perhaps that was the culprit and to change it again. I'm inclined to disagree with that because it's definitely working, unless I have the wrong one. The tech also checked the compressor and found it to be working properly and charged correctly. 
I am at a loss as to where to look next and could really use some advice. 
Perhaps you fine folks could lead me in the right direction. I would like to actually eat ice cream that is hard some day!


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## beenthere (Oct 11, 2008)

Does it shut off when it gets to 10, or does it keep running 24/7.


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## harryc (Mar 13, 2012)

beenthere said:


> Does it shut off when it gets to 10, or does it keep running 24/7.


I can't tell. There's too many fans running and another compressor next to it so there's too much noise going on to pinpoint.


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## djlandkpl (Jan 29, 2013)

Have you checked the temp with a different thermometer in case the one you have is inaccurate? If your 511 is like my 642, they share the same fan and evaporator coil. The only way you'll be able to tell if the freezer compressor is running is to pull the grill and touch/listen. If you hear the fan running 24/7, there's a problem.


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## zircon (Sep 24, 2007)

I feel your pain. For years and years I had a Sub Zero. It never really got cold enough. Poured money into it and the problem was never resolved and it cost a fortune in electricity. About five or six years ago I replaced it. I bought another SZ ONLY because it was the only thing that would fit in the space without redoing all the cabinetry. After several warranty calls to get the ice maker working, the unit, a 661 has been performing well and keeps cold. Based on my experience, I would never recommend SubZero. Totally overrated POS. One can buy four good refrigerators for the price of one SZ.


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## harryc (Mar 13, 2012)

If I were to discover that the compressor is in fact running constantly even though the thermostat was just changed last week then what would be the next thing to look for?


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## harryc (Mar 13, 2012)

djlandkpl said:


> Have you checked the temp with a different thermometer in case the one you have is inaccurate? If your 511 is like my 642, they share the same fan and evaporator coil. The only way you'll be able to tell if the freezer compressor is running is to pull the grill and touch/listen. If you hear the fan running 24/7, there's a problem.


Yes we have used several thermometers. Also a gallon of ice cream never freezes solid. In fact it usually looks borderline melted. 
I also noticed that when the defrost timer kicks in the freezer can go as high as 20 degrees during the cycle.


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## djlandkpl (Jan 29, 2013)

Just a guess. There could be temperature sensors in the cabinet that are misaligned or broken.


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## beenthere (Oct 11, 2008)

harryc said:


> If I were to discover that the compressor is in fact running constantly even though the thermostat was just changed last week then what would be the next thing to look for?


Compressor issue, or charge issue, or a restricted strainer, or a fan for teh freezer not working or spinning in the wrong direction.


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## harryc (Mar 13, 2012)

beenthere said:


> Compressor issue, or charge issue, or a restricted strainer, or a fan for teh freezer not working or spinning in the wrong direction.


Compressor working fine. Charge is perfect. (Tech looked at all this) the fan in the freezer blows properly. 
The tech thinks it's the defrost timer but I don't see how since it appears to work as intended. Is it possible that the defrost cycle is coming on too soon?
Could there be some other issue with the part that defrosts the coils


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## beenthere (Oct 11, 2008)

Only way to know charge is right. Is to recover it and weight it. Is that what he did.


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## harryc (Mar 13, 2012)

beenthere said:


> Only way to know charge is right. Is to recover it and weight it. Is that what he did.


There is no gauge that can determine the correct charge?


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## beenthere (Oct 11, 2008)

harryc said:


> There is no gauge that can determine the correct charge?


Nope. Specially on units that wrap the cap tube around the vapor line to serve as a desuperheater.


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## harryc (Mar 13, 2012)

beenthere said:


> Nope. Specially on units that wrap the cap tube around the vapor line to serve as a desuperheater.


Let's for the sake of simplicity assume the charge is correct (I didn't watch him work for 3 hours), and assume that both the thermostat and defrost timer are ok, what would be the next likely culprit to check?
By the way, I just read on another site that sub zero freezers do not take the moisture out of the air and attempt to keep the food no lower then 32 degrees to preserve the integrity of the food. Is that baloney or is there some truth to that?


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## beenthere (Oct 11, 2008)

No fridge keeps food colder then 32 degrees. It would freeze the food if it did.

Charge or restriction in the strainer.


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## harryc (Mar 13, 2012)

beenthere said:


> No fridge keeps food colder then 32 degrees. It would freeze the food if it did.
> 
> Charge or restriction in the strainer.


I've been playing around with positioning the thermometer in different spots of the freezer. The top shelf gets the coldest at five degrees where the bottom shelf isn't nearly as cold at 10-15 degrees. Even though the fan appears to be running could it be not circulating well? It seems to blow ok.


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## beenthere (Oct 11, 2008)

Its possible.


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## bilug (Apr 16, 2014)

Most likely it's an oil logged cap tube. We see this type of stuff all the time on Ultra Low Freezers (-80C).

You have to defrost them for at least 24 hours annually. Otherwise the cap tubes get built up with oil and they won't pull down to temp.

Try it...and see if it pulls down to where it should be.


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