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Cake day: December 4th, 2024

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  • Sorry for the impending refrigeration rant but I’ve seen a lot of dead chest freezers and small bar owners disapointed at that news so now I have been activated like a sleeper agent. Not dirrected specifically at you or even terribly applicable to the thread. Just a PSA for anyone who wants to mine my text wall.

    Yes, chest freezers can handle an occasional high temp pull down. The issue is how continuously/frequently they have to do it. As far as your example about loading a whole bunch of hot food in the freezer; people frequently kill them that way even today. Most people don’t realize that most chest freezers aren’t really designed to freeeze things; they are just designed to keep already frozen things frozen. It’s actually recommended that you initially freeze things in a standard freezer before you transfer those things into your chest freezer. For most chest freezers pulling things down to temp is not part of the design parameters and they usually will say that somewhere in the manual which no one reads because who needs a manual for a freezer.

    There are several reasons for this. Firstly, the refrigerant metering device on your average chest freezer is just going to be a capillary tube. Cap tubes are great because they’re just little tubes so they’re dirt cheap and there is nothing that can really go wrong with them if they don’t get plugged or broken. But they also suck because they are just little tubes so they don’t adjust to varried loads at all. They are designed for a specific box temp and a specific ambient temp. If the box temp is too high they just underfeed refrigerant and the whole system runs hot and poorly until the box temp gets down close to the design temp. The hermetic compressors used on chest freezers (and almost everything now) are cooled by the suction gas going back to the compressor. If that suction gas comes back significantly warmer than designed then the compressor will begin to heat up and eventually overheat entirely. Compressors are specifically designed for either freezer or cooler use at least in part due to this (also compression ratios). The compressor should have a thermal overload (the sole safety device on even many new chest freezers) that shuts it down when that happens but that’s just a safety device. That thermal overload is mostly there as a circuit breaker device in case the compressor is drawing too much power usually due to failed start components. If too much current passes through the overload to the compressor then it gets hot from it’s own heat like a normal circuit breaker and trips. It only somewhat serves as a compressor high temp cutout because it’s mounted on the compressor shell and when the shell gets hot enough it will also trip the thermal overload or at least make it easier for it to trip. However that is only sensing the external shell temperature of the compressor. The windings, bearings, and other internals get much hotter than the outer shell. They aren’t designed to repeatedly overload and doing so will lead to them progressively getting hotter and hotter until eventually the compressor fails due to overstressing the internals. Put it this way, when I encounter a compressor that has been repeatedly tripping the thermal overload, the compressor shell is almost alway hot enough to instantly flash water to steam and that is the coldest part of the compressor. Repeated overloads also destroy the start components. I actually just had to swap start components on a little freezer today because it tripped the thermal overload enough (failed condenser fan motor) to fry the start relay. Depending on the refrigerant and oil, the refrigerant or oil itself can also break down into a wax or even an acid under high temps which will plug the capillary tube or basically electroplate the compressor bearings with disolved copper from the pipes until they seize solid. R-134a which was a fairly commonly used refrigerant in smaller refrigeration appliances (typically fridges), is particularly bad about waxing up cap tubes. Also newer POE oils are actually much worse than the older mineral oils as far as potential acid issues go.

    Of course this is all assuming we’re talking about a plain old no frills chest freezers. There are fancier ones out there designed with higher performance in mind, but even today most chest freezers sold are the same big dumb boxes they were 40 years ago, just now with new refrigerants and sometimes digital thermostats. If you weren’t specifically looking for the fancy ones then I can almost guarantee that you have a big dumb box type chest freezer. I also still wouldn’t recommend using one of the fancier ones for this because it’s still outside design parameters. Even the multi thousand $ commercial units I work on aren’t really that much more than a big dumb box which will stab you in the wallet if you get too creative with it. You don’t get into much safety equipment or guardrails until you start working with walk-in units and even then they will frequently happily cause a $10,000 repair bill just because you didn’t use them quite right or catch a minor problem quickly enough or mercury was in retrograde.

    At the same time if you got a free/cheap chest freezer you don’t particularly care about and want to give it a shot then there’s not much reason not to try it. Science is always good as long as you know the potential repercussions. Worst case scenario there is you fry your free/cheap chest freezer and go back to plan A of not using the built in refrigeration. If it is well insulated enough and everything lines up perfectly then it just might work perfectly despite the odds. I do frequently run across equipment that leaves me utterly baffled as to how it could have possibly run for as long as it did under the conditions it was in. That could be this chest freezer battery box.