You are chilling the centrifuge with your solvent. One solution is to pull a vacuum on the jacket, which will insulate the internals from your 20C lab. Then prechill the centrifuge with dry ice or liq N2. If you run -60C fluid in the jacket, you end up with a giant snowball in your lab. Which has its own set of problems.
And you noticed that your freezer doesn’t have enough chilling power as well… ethanol has a specific heat capacity. You use that to calculate how much heat you need to remove over your desired timeframe. The size a chiller with at least that capacity.
Math is around here and labeled well.
Eg: Chiller question! Single or multi stage?? - #3 by Lincoln20XX