Sub-Zero Model 550 Thermostat Replacement <Also, refrigerator Icing Issue>

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Old 08-06-16, 11:27 AM
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Sub-Zero Model 550 Thermostat Replacement <Also, refrigerator Icing Issue>

A few years ago I initiated this thread when I had a temperature control problem with my freezer...

http://www.doityourself.com/forum/el...shuts-off.html

Zoom ahead 3+ years, I still have the replacement thermostat (p/n 7014665) in a box, and while the freezer has never shut off entirely for an extended time, I still have temperature control issues (i.e. temperature changes without adjustment of thermostat).

So I'm thinking I should go ahead and finally change it out. Anyone have any idea what's involved to do that?

One other note, probably unrelated... During the summer, the lower, back left corner of the refrigerator often ices up on the vertical back panel. Any thoughts on this?
 
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Old 08-07-16, 12:28 AM
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Here's a link to a service manual that illustrates the control replacement.
Sub-Zero_Built-in_500_Series_Refrigerator_Service_Manual.pdf

Not sure what the issue is with the frosting problem.
 
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Old 08-07-16, 11:40 AM
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Thanks for the link Pete. Looks like the info on replacing the thermostat starts on page 26.
 
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Old 08-17-17, 06:36 PM
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One year later, I still haven't gotten around to swapping the new thermostat in. I never had a repeat of the total defrost, but I do once again have ice build up in the lower-left of the fridge.

Pic attached. Any thoughts on what might be going on here?
 
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Old 08-17-17, 07:14 PM
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Frost buildup on the outside of the evaporator cover is usually caused by a defective door gasket.... especially along the bottom.
 
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Old 08-18-17, 06:45 AM
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Thanks for the reply Pete. The fact that this only occurs in the warmer, more humid months would indeed seem consistent with a door gasket seal leak. Well, that and someone leaving the door open too long!

Are you assuming that this is where the evaporator is located, or do you have specific knowledge that it's located in the back-left on this unit?
 
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Old 08-18-17, 01:37 PM
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In the manual link I left you..... it looks like both coils are down low.
See illustrations 2-66 and 2-67.

If it's not the actual coil area then it may be where the cold air exits.
It needs to be the coldest place for the frost to form.
 
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Old 12-04-18, 07:44 PM
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Nearly Six years ago I posted this message...
https://www.doityourself.com/forum/e...shuts-off.html

And followed it up a couple years later with the thread I'm updating tonight. I finally installed the freezer thermostat!

Too soon to know how things will work - I'll update after it's been running for awhile. I also wanted to post an updated link for the service manual since the one posted previously has gone away.

https://www.manualslib.com/manual/79...page=27#manual
 
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Old 12-04-18, 08:16 PM
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Ahhhhhhhh.... there you are for your yearly visit.

Thanks for the new link. The other site closed up shop which happens fairly quickly.
 
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Old 12-05-18, 08:25 AM
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The nature of the problems weren't so bad as to motivate me to replace the thermostat. But now I was/am having a couple issues - increasing ice build-up in the freezer, mold in fridge, and water leaking from bottom.

So I decided it was time to fully defrost, clean, and replace the freezer thermostat.

The mold was much worse than I had ever imagined. The bottom tray was full of it; Black mold on the floor under the fridge and walls. It looked like something you see in an abandoned house!

I thoroughly cleaned everything including the drain in the back of the fridge with a long zip-tie. I'm not confident all my issues will be solved, but we'll see where this takes us. I should probably invest in new door seals, but for now, we'll see.
 
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Old 01-11-19, 08:46 AM
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Just a quick update.... The new freezer thermostat seems to have done nothing for my temperature control problem. I had the freezer setting around 4.5 and all seemed to be okay for a couple weeks, and then one day my ice cream was soup! I cranked it up until I heard the compressor kick in at a setting of about 6. It's been okay for about 5 days since setting it there, but who knows.

And no, the freezer door wasn't left open. Such a weird issue to try and diagnose. Any ideas what else to try, short of shopping for a new fridge?
 
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Old 06-12-19, 08:04 AM
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DPD, I have a 550 exhibiting similar symptoms. Freezer was working fine and I made the mistake of adjusting the setting which was very difficult as the knob would barely turn. I freed the nob with a bit more effort and that seemed to set off this episode. Now if a turn the knob to say "6" the compressor will kick on and bring the freezer down to 0 to -5 F, so all looks good. The issue is once it does cycle off it does not appear to want to cycle back on. I got up this morning and both compressors were off (temps good in both compartments). So I waited to see if the freezer would kick back on. Temps in freezer rose to low 30's and I got impatient and turned the dial down and back up and the compressor kicked back on. So as best I can tell the bimetallic element in the thermostat is failing to kick the power back on to the compressor. I guess I will be following your replace the freezer temp control journey and hope that fixes the issue. Don't think it is a faulty defrost timer as the compressor will cycle on with knob adjustment. Also don't think it is the defrost terminator.

Any tricks on replacement would be helpful. I'm familiar with back panel removal as I have replace the refer side control. Question: assume sense wire goes down into freezer section, but does wire wrap around the evaporator coil somewhere or clip?
 
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Old 06-12-19, 10:47 AM
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As far as I know the freezer thermostat is a two wire device so it's either on or off. If you've replaced it and it's not functioning correctly..... it may be bad too.

Not familiar with the freezer stat replacement but it's very important to have the thermostat bulb in the correct location.
 
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Old 06-13-19, 08:05 PM
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Replacing the thermostat wasn't terribly difficult. If you possibly can, I'd suggest emptying the fridge/freezer and giving it a full defrost and cleaning. I had a lot of black mold to deal with due to a clogged drain I believe.

Back to the thermostat, it took a little effort to get the old one out and the new one in, as it goes down a conduit tube in the back. I don't recall it clipping into place at all - it's just the conduit that secures it.

Several months later, I'll say my freezer temperature control is better, but still has occasional random temperature spikes up for no apparent reason. I'm also again seeing some ice build-up on the lower-left back panel.

I am not a fan of Sub-Zero.
 
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Old 06-13-19, 08:26 PM
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Ice buildup could also be caused by a leak in the evaporator and the freezer system getting low on refrigerant.

Very important on Sub Zero's to keep the condenser coils up top clean.
 
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Old 06-14-19, 08:55 AM
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I should be more clear... The ice build-up is in the fridge, lower-left corner. The refrigerant fittings are both up top by the compressors, right? On a circa 1994 unit, they would be R-22, yes?

Condenser coils up top are indeed cleaned on a semi-regular basis.
 
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