• Please note, some of the links on our site are affiliate links (Learn More)

FIXED Sub-Zero 550 Freezer Icing - Why was it caulked?


Premium Member
Sep 27, 2021
Model Number
More than 10 years
My parents have a 30 year old Sub-Zero 550 with major ice buildup all down the right side of the freezer. After doing a little research, I ordered the drain heater kit (4202160) and plan to install it the next time they defrost it. Other than that ice buildup (and a small amount on the bottom of the fresh food section) the fridge works fine.

I haven't taken the evaporator cover off to look yet, so I don't know if a drain heater was already installed. I see that the right side of the cover was caulked at some point (picture attached).

Right now, my questions are:
  • What was the reason for the caulk?
    • Was it probably something a tech did?
  • Was it an actual fix for water going down the side and freezing?
  • When I replace the evaporator cover, should I caulk it again?


  • IMG_0057.jpg
    151.8 KB · Views: 122
Caulked at the factory----Yes but not for the drain freezing---yes--- check @surfer349 two treads about this to see what you might be in for That's a sloppy caulking job, someone's been in there before.
Thanks for pointing me to those threads. I'm definitely not pulling it out and cutting a hole in the side - if I can't get the new heater in the drain tube, I'll bail. The good news is that there is never frost on the evaporator, just down the right side, so the defrost works.

Should I caulk around the evaporator cover after replacing it? Just trying to be ready before I tackle this.
Took it apart today and found that there was a drain heater installed already. Same ohm reading as the new one (~900 ohms). I don't think it went all the way down.

We sent lots of hot water and soap down and it finally cleared. Now it flows down easily. But we figured we would try to replace the drain heater anyway (since we had the new one) and it broke pulling it out. Now half of it is stuck in there. I don't think it's going to budge, at least not without some tool we don't have (angled pliers?).

So, it won't have a drain heater for now. I can put in a piece of control cap tubing touching the heater. Where could I get that?

Thanks again for the great help!
You're in the same boat as surfer349. You can look underneath to see if any of the cat gut is sticking out of the drain and try pulling it out from there. Oh, and better unplug that heater.
Success! Borrowed some angled needle nose pliers and we were able to get the rest of the old drain heater out. The end of it was cold, even though we had put lots of near-boiling water down the tube. Just goes to show that however much time/water you think you need to get it defrosted, you need more. Got the new one in and we'll see if the ice returns in a month.
success? I had to pull my unit out and cut the exterior wall because the heater wire was completely stuck in the drain pipe. It wasn't that bad at all.
Sort of. I was able to get the drain pipe cleared out, and replaced the old heater wire with a new one. Both the old and new one tested good (900 ohms). I think the only real improvement I made was clearing out the drain pipe.

About a month afterward, the ice along the right side returned, but now it appears to have subsided on its own. I can't explain this. If it does return, what else can I do? Replace the door seal? The freezer door seal has a tear along the top, but it does appear to still seal well and is hard to open after closing (the suction effect).
No frost on the evap cover, just down the right side. I did recaulk - I did at least as good a job as whoever did it last :).

Right now it seems okay (knock wood) but what should be our plan if it ices up badly again?
Frost or that ice drip? See the link in my earlier post. Sadly even that doesn't always work, that drain tube is just too small. I even tried a 6HR 21Min defrost timer, yours is probably a 24HR comp/run timer(depends on ser#)
It's an ice drip, not frost. Solid ice. I'll take a look at the serial next time I'm over. Did the different defrost timer help?

Pulling it out seems like it would be difficult as it is mounted up on blocks, so the wheels are a few inches from the ground.
If you feel that you have benefited from this site, and would like to show your appreciation.