Freezer Thermostat

I have a commercial freezer, the thermostat shorted out two days ago.

Repairman comes and puts in a new thermostat.

Now the freezer does not get below 10 degree Fahrenheit even when the new thermostat is set to be -30F when before I had it set at -10F.

Any ideas what might be the problem?

You didn’t say, specifically, what was wrong with the old t-stat and ‘shorted out’ can cover a lot of things if you don’t know what you’re talking about. It’s possible the t-stat wasn’t the issue, but it’s cheap and easy replace to replace so your HVAC guy may have started with it instead of checking other things as well.

What’s happening (right now)? Is the compressor shutting off? Is it just running continuously trying to get to -30? We should probably just start with that.

How do you know it’s at 10F? Do you have a thermometer in the case?
If you do, you can spin the t-stat back and forth and see if it clicks at the same temp that the thermometer is reading.

I should mention that t-stats tend to be unreliable WRT the temp on the dial. I always keep (in my coolers) a regular thermometer. In my freezers I can tell my how solid everything is. Then I adjust the t-stats based on that, not necessarily the numbers on them.

There could be some other things to look at, but right now, I’m more interested in the above questions.

I believe it was the thermostat as it actually melted.

As far as I know the compressor is constantly running.

The back of the condenser is starting to ice up and feels much colder than the air of the freezer, maybe not -10 though.

I have a thermostat in the freezer that tells me it’s 10F

Well, that’s not good. Let’s just assume, for now, that it went bad on it’s own.


Check (thermometer, right)

I assume you mean evaporator, the part inside the freezer, right? The condenser is the part on the outside.

Okay, this is where it gets interesting. It could be icing up for lots of reasons. It could be icing up because it’s low on refrigerant. This will also cause it to not run as cold as you’d like it to. Take a look at the ice pattern. Is there a big chunk on one part of the coils, but the rest are most clear. Could be the top, the bottom, the left or right, but mostly in one area and concentrated around the TXV.
It could also just be iced up because it’s been running nonstop, or if there’s a lot of humidity in the air, or if your defroster isn’t working properly.

Ice blocking the coils will make it difficult or impossible for the freezer to maintain temp. Ice forming around the TXV (and/or it’s bulb) OR ice formed around the t-stat bulb will cause all kinds of wonky problems.

The first thing you might want to do is see about getting rid of that ice. There’s a handful of ways to do it, I can give you some ideas. If it’s possible, sometimes the easiest way is to unload it and let it thaw on it’s own.
Sometimes it’s to run it through a few defrost cycles.
If the evap coils are on the bottom, buckets of warm water are usually fastest, but keep in mind that all that water is going to pour out the bottom if it doesn’t have a drain plumbed to the outside.

But, just for kicks, make sure none of that ice is formed around the t-stat bulb (which may be snaked inside the coils), if that’s the case, the t-stat thinks it’s 32 degrees and that’s probably your problem.

The problem is that that you have a lesser performing heat pump now.

The symptoms you list (ice forming around evaporator, compressor running all the time, never got cold) happened to me once.

Ends up, the door wasn’t closed all the way.

Think I figured it out.

The repairman put the new thermostat bulb directly behind the evaporator.

I replaced the bulb down to the bottom of the freezer, it’s now at -5…still not cold enough but close.

You think there is still an issue on top of this?