Refrigerator too cold and frosting over

October 11, 2021 10:38 AM

My fridge is freezing the food at the bottom, but seems not that cold at the top. What gives?

We have Subzero 685, which is about 15 years old. Last week, the back of the fridge developed a thick layer of ice and frost. The food in the lower 1/3 of the fridge also froze, even though the temperature readout says 38F. After trying a few different ways to de-ice it, I wound up taking off the entire back interior wall so I could see the evaporator coils. They were caked in thick ice. I de-iced everything and restarted the fridge without any food in it except for a cup of water at the bottom.

When I restarted the fridge around 5pm last night, the internal temperature gauge said 83F. It has been running for about 15 hours now and the internal gauge says 55F. But, the cup of ice at the bottom of the fridge has frozen. The evaporator coils have a little bit of frost, but not a lot.

I'm not sure what is going on. It seems like the evaporator coils may be running way too cold, and freezing everything near them. But on the other hand, the rest of the fridge does not seem that cold. Maybe the temperature sensor is broken? But the sensor is placed higher up in the fridge than where it is getting super cold, so maybe it is fine. The fridge does not feel like it is 32 degrees in the top 1/2, though the water is freezing at the bottom.

The door seal seems OK, although there is a small ~1 inch tear in it at the top of the fridge. The fan blows when I close the door. The compressor seems to be putting out tons of cold (too much). I had the compressor coils cleaned within the past ~4 months and the service guy said that this model should last 20 years. What am I missing?

posted by Mid to Home & Garden (9 answers total)

The 38f is I think what the fridge is trying to achieve as a target temperature, I suspect the reason it's getting so cold is it can't achieve that temperature (as read by the sensor high up in the fridge compartment) because of some ice build up or blockage elsewhere in the system, possible in the evaporator drain. In my experience this feels sort of like the de-icing wasn't completely effective and there is a blockage in the drain from the defroster to the evaporator pan that is usually under the fridge itself.

At the end of the day the unit is trying to do what it should - get things cold (i don't believe there is a "too cold" for this kind of thing, it's a binary on or off thing) , there is likely some icing up in the passage between the freezer compartment or the refrigeration coils to the fridge compartment that is preventing cold air from being effectively transferred. I'd also check and see if there is a fan in the fridge compartment that should be circulating air and figure out if that is working - perhaps when you de-iced it a connection got knocked loose ?
posted by iamabot at 11:40 AM on October 11, 2021

The temperature sensor and the de-icing heater are burned out.
posted by The_Vegetables at 11:41 AM on October 11, 2021 [1 favorite]

There are a few fans that all need to move air around, so you may not be hearing the right one. I had similar problems to you -- too cold on bottom, warm up top -- when our evaporator fan was dead.
posted by Dashy at 12:06 PM on October 11, 2021 [1 favorite]

The_Vegetables likely has it. Although it could be either one (as opposed to both) of those parts. Of the two, the de-icing element is more likely to have failed organically at 15 years, as it’s basically a light bulb. The other possibility is that a condensate line has gotten blocked. Either way you need a tech for this unless you’re comfortable taking things apart.
posted by spitbull at 1:29 PM on October 11, 2021

Check that the door seal is not damaged or out of place before worrying about more complicated problems. If it is sealing well, earlier answers have good ideas about what to investigate.
posted by wierdo at 2:25 PM on October 11, 2021

Response by poster: Thanks, a couple of additional facts/points:

1. I don't think it has a defrost element in the fridge. The manual says that it relies on pauses in the cooling cycle to defrost in the fridge. It has an element in the freezer.

2. It has separate compressors for fridge and freezer.

3. I think it only has one fan that circulates in the fridge. That fan spins when I hold the "door close" buttons down.

4. I have not checked the water drain line/pan under the fridge yet, but when I defrosted the fridge all of the water ran down the little drainage trough without a problem, so this seems OK?

I ordered a new termp sensor - it was only $10, arrives tomorrow. Hopefully that is it, although I don't think it is. The problem seems to be related to circulating the cold air around the fridge and/or possibly losing cold air through a bad seal.
posted by Mid at 2:48 PM on October 11, 2021

You can get one or two fridge thermometers and see what those readings are.
posted by calgirl at 7:45 PM on October 11, 2021

Response by poster: A little more info -

After running for a day, the bottom 1/3 of the fridge is at like 32 degrees but the top part is no colder than 55-60. Food freezes at the bottom. I figured out how to get a diagnostic report from the two temperature sensors in the fridge - the one in the upper part of the compartment shows warm temps (55-60) and the one that is mounted next to the evaporator fins near the bottom is extremely cold - like around 10 degrees.

I guess what is happening is some combination of: (1) air is not circulating inside the unit - not sure why, the fan at the top seems to be running fine when the door is closed; (2) the compressor is running all the time, maybe because the top 2/3 of the fridge is warm; (3) this makes the evaporator really cold and freezes it over - the defrost system depends on a cycle of turning the compressor off for a while, but that isn't happening; (4) the ice build-up on the evaporator is hurting the air circulation.

It doesn't seem to be a temperature sensor problem - the sensors seem to be reporting correctly, at least directionally (really warm and really cold). It seems more like an airflow problem - the cold air isn't getting to where it should go -- but that's about all I've got. I'm about to throw in the towel...
posted by Mid at 8:19 PM on October 11, 2021

Response by poster: I think I have it figured out - it's mainly that I'm an idiot. When it first froze over, I took the back wall off the interior of the fridge so I could de-ice the evaporator with a hair dryer. I left the back wall off, thinking that I could observe the evaporator and watch for ice with the wall off. It slowly dawned on me that the back wall is an important part of the airflow system - I don't really understand why, but the back wall somehow channels the airflow from the fan at the top to the evaporator toward the bottom. After I put the wall back in, the fridge quickly reached 39F and seems to be staying put.

So, bottom line - I think we left the door open one night and froze the whole thing over, then I did the right thing by de-icing the evaporator, but then I messed it up by leaving the interior back wall off, which messed up the airflow. All good now, I hope.
posted by Mid at 8:26 AM on October 12, 2021 [1 favorite]