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Hi, for the last few weeks, i have noticed that my unit fan was running all the time. After reading a number of online resources i have found that my evaporator is completely blocked with ice. I used a hair dryer to defrost and was hoping the issue will be resolved. Unfortunately, it kept coming and every a week or two i had to defrost it. finally got someone to look and was told to replace the door seal, which i did. After a couple weeks the issue came back or was still the same. I was told that the sensor might be damaged, or the board. attached please find the pictures of before and after: https://ibb.co/cdjPvkhttps://ibb.co/jrqWakPlease help. Thank you
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I haven't worked on sub-zero in years, so maybe another tech will know better that a certain part is known to fail. But I'll do the best I can based on basic techniques. It's clearly not defrosting itself properly. There are 3 main reasons that ice builds up and is not defrosted: 1) The defrost heater is open - meaning no current passes and hence no heat 2) The defrost termination thermostat is open. It opens to stop the element from continuing to heat at a set temp, probably ~50deg. If it fails close after it cools back down - no more defrost. 3) The control board is not asking it to defrost. Harder to diagnose. You'd have to be able to put it into defrost to tell. My bet is #2, possibly #1. Hopefully not #3. There's more reasons like a clogged defrost drain or bad defrost thermistor but we'll hold on those for now. Here's a manual for your machine: https://www.manualslib.com/manua...eries.html?page=5#manualdirect link to a pdf on my Drive storage if that site annoys you: https://drive.google.com/file/d/...d2F6c1U/view?usp=sharingpg 10-6 shows you a decent wiring diagram, with a multimeter you can use it to test the various components of the defrost system. I'd test at the element if possible but you can also do from the control end. The troubleshooting guide says that heater should be 20ohms. If it is oL or very high it is bad, although that type of element is not common to fail. In your de-iced pic the 2 black wires on the same plug are the element, unplug them and test the element side of that plug for resistance ~20ohms. You can also test defrost terminator at the same time; but only if it is iced up as otherwise that terminator may be open due to temps. On that plug there are a black and blue wire. Put one probe on the black terminal and the other on one of the blacks going to the element, (plug element back in for this). One of the element blacks will give little to no resistance as it is the loop back to the terminator and the other should be similar to whatever the element alone reads.  The arrow I added for the element plug is a little too long, it is meant to indicate the plug with 2 larger black wires behind the other plug. Good luck! EDIT!---PLEASE TURN THE MACHINE OFF WHILE DOING THIS! IF IT DECIDES TO DEFROST WHILE YOU'RE POKING AROUND, YOU MAY GET A NASTY SURPRISE. TESTING LIVE IS ONLY AS A LAST RESORT OR FOR THE VERY CONFIDENT OR FOOLHARDY.
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Rank: Member
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Wow. Thank you for the detailed information.
Once I am done with testing the unit, is it fixable or replaceable?
I spoke with Sub Zero and was told it could be 1 of 3: 1. Board, 2. Defrost heater, 3. Defrost terminator.
There is a function that allows a manual defrost (long press on the ice maker button) - after trying that it didn't work which apperantly eliminate the possibility of board malfunction.
So I am left with one of the 2.
Would the reading be helpful to know which one cause he issue?
Thanks a lot for the help.
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Rank: Member
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Tested and showing 0 OHMS black to black for the defrosting terminator.
Also, EC 20
Error Code: -20
-20 = Zone/Compartment thermistor fault – Repair wiring or replace thermistor
Any thoughts?
Thank you
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Rank: Member
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That's not a bad error. The thermistor is an easy fix. It's right up near where you tested the safety. Please verify that the element also tests normally as sometimes those errors are generated by the control pcb just not seeing values it expects. Meaning that it could be looking for a thermistor value that would equal 45 degrees after X amount of minutes. And not seeing that it shuts down to frost and generates that code. But the simplest answer is usually the right one so you probably have a bad thermistor.
The computer uses the thermistor value to judge when to end defrost. So if it is not seeing the temperature at the top of the evaporator accurately it may not be allowing it to defrost. If you can verify that the heater is intact and reading as it should then the thermistor is probably bad.
That should be a pretty easy change. When I am back on my computer I will point out on the picture where the thermistor is.
Having access to the service manual is invaluable when you are trying to diagnose things yourself. You've done well to get that error code out.
So if you can verify that the element itself reads about 20 ohms then I think with a large degree of confidence you can change that thermistor and fix the problem.
Good luck!
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Thank you again. Element reads 20.4 OHMS and terminator 00.4 OHMS (u it is completely frozen in both cases).
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Rank: Member
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You're very welcome! Oddly I enjoy this stuff... the way I see it is "it's a machine it can be fixed and I intend to fix it!" Those readings are good. I missed that you could turn on defrost manually, when you did that the element did not get hot? It may take 5-6 minutes and may not glow like an oven element but it should have gotten hot if turned on manually. Try that again and see if the 2 black leads show 120v potential across them. If not it is not powering the element. The annoying part: I do not know if the board will turn on the element in test and ignore a bad thermistor value, it's an annoying part of computerized appliances, we just don't know what the software will do except by trial and error. I'd think it would allow you to turn it on and off but who knows??? I assume you found the test mode and ran through the steps to find that it doesn't like the freezer evap thermistor? It looks like it is the small black cylinder with blue wires leading to it at the top of your pics. I can't find a resistance chart for it. Resistance through it changes as temps change and that is how the machine determines evap temperature. If you got that error than go ahead and change it, it isn't too $$ and certainly far less than calling one of us out. You can test it's resistance too, but without a known value it would only tell you anything worthwhile if it was totally open. At this point you may be more familiar with that unit than most techs as they are rare. My company doesn't even touch Sub-Zero/Wolf units as parts are hard to come by. You'll have to call them to locate an official dealer and it'll probably be far away and get shipped. I can't even find a parts diagram to be sure but it looks like it is part # 4204150 and available online; e bay and amazon both have what looks to be it. This site doesn't have it as far as I can tell. This one looks to be factory as it includes the plug, others you will need to splice in, not a big deal but why do it if not necessary? https://www.********.com/p/genui...1?_trksid=p2047675.l2644replace the ***s with e bay or just search by that part #. Good luck, and hopefully I'm not way off base on my diagnosis! Drew
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Rank: Member
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Thank you so much Drew.
Tried few times the manual heat. It didn't work. As advised by the Sub Zero tech support it can only be one of the 2.
I already ordered the defrost terminator and completely missed the Thermistor.
Just ordered it now.
Thanks a lot for the help.
I will post the solution hopefully as soon as I get the part/s replaced.
Have a great evening.
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Rank: Member
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Assuming that you can manually activate freezer defrost you should see voltage at that heater if the board is closing the relay. I'm definitely curious as to the fix. From what you tested I don't see how the termination thermostat could be bad but maybe it's opening at a low temp.
Good luck and let me know how it goes.
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Rank: Member
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Drew, finally got the parts. Replaced bot of them and let it run for few days. Unfortunately, still the same issue. I think it might be the heating element.
I also saw a correlation between how fast ice getting on it to running the ice maker.
(Running the ice maker will clogged the unit with ice in less than a day)
Any thoughts on that?
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