501F Sub Zero freezer ice build up in drain pan

[Ned.B]

Model Number

501F

Brand

Sub-Zero

Age

More than 10 years

Before I start into this, please note that I am not trying to DIY this repair, but before bringing out the repair company yet again, I want to have a better understanding of what might be going on. We've been working with the same tech for all of the repairs. The primary issue is with the freezer but the functioning of the refrigerator isn't perfect either. Please excuse me if I don't properly describe all of the repairs.

We have a 30 year old pair of 501 Sub Zero Refrigerator/Freezers. Both generally functioned when we bought the house a couple years ago, but had internal climate control issues. The refrigerator had issues with internal moisture and minor mold growth and the freezer had some ice build up.

Refrigerator:
We initially had the repair tech look at the refrigerator. They added an additional thermostat as it was assumed that internal temperature differentials were causing the moisture.
A few months later we realized that the constant flooding of the bottom shelf of the refrigerator was due to a frozen drain pan. They replaced the defrost heater about a year ago and haven't had that issue since.
However we started having issues with ice build up on the back of the refrigerator, and behind the back panel. They came out, reviewed several times, removed the ice, made a few minor component adjustments, but never really solved the problem. By trial and error we determined that whenever the kitchen temp raised above 70 degrees, we had to lower the internal temp from 5 to 3. While set on 3, we never have ice issues, but the internal temp measures at around 42, which is higher than we would like.

Freezer:
The freezer had internal ice and freezing issues also. The tech replaced both defrost heaters. The week after the heaters were replaced the compressor failed and had to be replaced. The new compressor had some sort of fault and also failed but we have not had any issues with that since.
However, the ice issue doesn't seem to have gone away. We realized late last year that the lower drawers were starting to get stuck. This was because the drain pan had completely iced over and had iced the bottom shelf as well. The tech came out dethawed the interior, and made a few adjustments. He thought that it was odd that it had taken months for this to happen and that it may have just been an unusual circumstance. But now less than 2 months later the drain pan is frozen again and is starting to overflow.
So main question is: what else can be done? What else should they be looking into?

Also before anyone asks the rational of repairing versus replacing units of this age, it was the tech's recommendation to repair versus replace as any of the components could be easily swapped out. Also due to the dimensions of these legacy units, any new refrigerator (and due to cost we would not do another 6' wide built in) would require an extensive renovation of at least one side of our kitchen.

Thanks in advance!

 

[rickgburton]

The freezer evaporator uses a defrost heater and a drain tube heater. The defrost drain water is caught by the V-shaped drain trough. Because of the the colder temperatures, a drain trough heater keeps the area warm during the defrost cycle only. If the heater for the drain tube is good and the drain trough is icing over the drain tube needs to cleaned out.

The refrigerator evaporator doesn't use a defrost heater. This evaporator coil incorporates an off-cycle defrost. Once the system is pulled down and the control is satisfied, the unit is shut down. The unit will remain off until the 39° F cut-in temperature is reached at the control.

A frost issue on this evaporator is caused by either a sealed system issue or cold control issue. A refrigerant leak can cause an abnormal frost build up and since you had the compressor replaced that's the first place I would look.
Water in the refrigerator section is usually caused by a blocked drain line.

The tech came out dethawed the interior, and made a few adjustments.

made a few minor component adjustments,

Other than turning the cold control knob colder or warmer, there are no adjustable components in this machine.

 

[mistateo]

Before I start into this, please note that I am not trying to DIY this repair, but before bringing out the repair company yet again, I want to have a better understanding of what might be going on. We've been working with the same tech for all of the repairs. The primary issue is with the freezer but the functioning of the refrigerator isn't perfect either. Please excuse me if I don't properly describe all of the repairs.

We have a 30 year old pair of 501 Sub Zero Refrigerator/Freezers. Both generally functioned when we bought the house a couple years ago, but had internal climate control issues. The refrigerator had issues with internal moisture and minor mold growth and the freezer had some ice build up.

Refrigerator:
We initially had the repair tech look at the refrigerator. They added an additional thermostat as it was assumed that internal temperature differentials were causing the moisture.
A few months later we realized that the constant flooding of the bottom shelf of the refrigerator was due to a frozen drain pan. They replaced the defrost heater about a year ago and haven't had that issue since.
However we started having issues with ice build up on the back of the refrigerator, and behind the back panel. They came out, reviewed several times, removed the ice, made a few minor component adjustments, but never really solved the problem. By trial and error we determined that whenever the kitchen temp raised above 70 degrees, we had to lower the internal temp from 5 to 3. While set on 3, we never have ice issues, but the internal temp measures at around 42, which is higher than we would like.

Freezer:
The freezer had internal ice and freezing issues also. The tech replaced both defrost heaters. The week after the heaters were replaced the compressor failed and had to be replaced. The new compressor had some sort of fault and also failed but we have not had any issues with that since.
However, the ice issue doesn't seem to have gone away. We realized late last year that the lower drawers were starting to get stuck. This was because the drain pan had completely iced over and had iced the bottom shelf as well. The tech came out dethawed the interior, and made a few adjustments. He thought that it was odd that it had taken months for this to happen and that it may have just been an unusual circumstance. But now less than 2 months later the drain pan is frozen again and is starting to overflow.
So main question is: what else can be done? What else should they be looking into?

Also before anyone asks the rational of repairing versus replacing units of this age, it was the tech's recommendation to repair versus replace as any of the components could be easily swapped out. Also due to the dimensions of these legacy units, any new refrigerator (and due to cost we would not do another 6' wide built in) would require an extensive renovation of at least one side of our kitchen.

Thanks in advance!

If you still have this sub zero 501 set, I MIGHT be able to help. Like you, I inherited my set when I bought my house and have battled to get them performing right.

For the fridge, as rick mentioned above, there is no defrost "heater" like the freezer. The thermostat (which you mentioned was replaced) turns on and off to maintain the correct temperature range. Just need to make sure the drain tube remains clear. If you STILL get frost build up that isn't going away, have a qualified tech ensure the refrigerant level is correct. Also important to ensure the evaporator and condenser fans are working properly, and the condenser coils are not choked up with dust.

For the FREEZER, I'll cut to the chase: it has FOUR defrost heaters. The large obvious one that snakes through the evaporator coil (2.1 ohms), the steel wire loop in the drain tube (900 ohms), a small black one on the ice maker fill tube (2600 ohms, only on later models), AND one that is stuck onto the BOTTOM of the drain trough with adhesive (260 ohms). Ensure all heaters are close to the specified resistance. I only found out about that fourth heater because of a parts diagram: https://www.guaranteedparts.com/picture_library/Subzero/Subzero-500 Series/501F.pdf

It is listed here as part number 3013530 (Drain Trough Heater). The new part number is 7006289. I got mine through my local sub zero authorized parts dealer, which varies depending on which region you live in. It is kind of a pain in the butt to replace. You must remove the shelves, the evaporator cover, the bottom glass shelf with the 4 screws, the ice maker assembly, the cover for the wiring under the drain trough, and finally the drain trough itself. Then you need to scrape off all the silicone caulk from the drain trough and the freezer wall and remove the old trough heater by peeling it off like a big sticker, hoping it comes off as one piece, then clean up the adhesive residue. Stick the new one on, then screw the drain trough back in place, re-caulk and reassemble the rest.

Before I replaced my drain trough heater, I had to defrost the entire freezer unit like every 3 months. Now that it has been replaced, it has not frozen over since. Hope this helps!