pushing the limits on a cheap chest freezer?

Has anyone wired in a Temp controller to bypass a factory t-stat to get their cheap deep freezers colder? What is the chilling “limits” of standard R134a refrigerant in a chest freezer? ive read online in homebrew websites and PC benchmark / overclocking crowds that getting below -20F could potentially create a vacuum on the low pressure side of the compressor? i have also read that people have gotten R134a window ac’s to cool below -40f but these are often in short bursts bursts during overclocking PC benchmarks. I would be interested in know if its possible to get a chest freezer to cool around -30f to -40f using the stock refrigeration R134a system for a few days at a time simply by bypassing the stock tstat and wiring in an ebay temp controller to run the compressor longer.

Interesting notion. What you are asking is basically can you turn on the compressor without modifications to the compressor and have it behave in a higher performance mode by simply bypassing circuits meant to shut it off.

The problem with answering such a question becomes then precisely what is the thermostat either turning on or off in order to regulate temp? Does it kill power or does it move a valve or ???. A schmatic would be needed to first understand fully exactly what you would be bypassing. Certainly a hot water tank comes equipped with an emergency pressure relief valve that opens before the system explodes. Could removing the valve allow for higher pressures? Likely… until the system it was meant to protect fails.

I love tinkering and would enjoy seeing somebody pull off making an ultra low refigerator out of something that is not lolz. Sounds like something my Dad would have tried at some point. It is a good thing you have an inexpensive model to attempt this on. There will be a failure because without any doubt in order to achieve what you wish the compressor will likely run 100% of the time. A 100% duty cycle not built into the unit but being pressed into service this way will fail the unit.

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For the record i like doing things as cheap as possible. im only a med patient/caregiver in Maine so doing things as cheaply as possible is very appealing to me. On another note i recently picked up a Neslab CC-100 immersion chiller for 500 bucks, not sure how ill implement it yet lol.


i dont know enough about refrigeration systems to make “safe” decisions but im irish and scottish so i think ill mess around with it a bit anyways. From what ive comprehended from reading online the higher the working pressure the colder it can go (i dont know if this means on the discharge or inlet of the compressor). i wonder if tuning the system (adding a little bit more R134a and bumping the pressure 1psi at a time in the low or high side line) coupled with longer compressor cycle on time would give the desired effect… i guess it couldnt hurt to experiment lol (or could it haha). its simple enough to wire in my own controller and start off with running up the compressor for an extented period of time to see how low it can go in stock trim.

Pressure/temp ratio of R134a https://www.forane.com/export/shared/.content/media/downloads/products-documentations/fluorochemicals/forane-134a-pressure-temperature-chart.pdf

I believe the tstat may have a simple pcb that will keep it from kicking the compressor on right after shut off but its just powering a relay to power the compressor. either on or off. theres not actuated or electronic/control valves or anything that im aware of.

With a simple tstat mod I have am seeing -24.5f as the coldest I can push it. This may be the limit of the freon used in the freezer.

most likely you are seeing the limitations of the pump.