Using a Refrigeration Compressor As a Vacuum Pump

I use two compressors from dehumidifiers to pull for the vacuum system for my Stubby lathe. Mine have been working just fine for four years now and pull about 28" of vacuum. I get the compressors for free from an appliance shop who are glad to give me their junk after the Freon™ has been removed. I therefore have several spare compressors on the shelf in case one in my set-up fails.

The pic shows how the compressors are set up. They have since been enclosed in a box with the fan drawing cooling air through a small furnace filter at the opposite end to keep things clean inside. The whole thing runs nice and quiet. Note that a refrigerator compressor might work for say a veneer press, but you'll need a much bigger unit for a lathe because these closed loop compressors pull rather low CFM. That's why I use two, taken from 50-pint dehumidifiers or at least a 2+ ton window A/C unit, so that I've got almost 5 CFM in draw to compensate for wood porosity.

Do note, however, that you must have a small fan blowing on the compressor housing(s) during use because these compressors have internal thermal overload disconnects that will trip and shut them down after not many minutes unless cooling air is used. In A/C or dehumidifier units, the heat exchanger/circulation fan does the job, but in stand-alone use they need supplemental air movement. If they get hot and stop, you get to follow the bouncing bowl in your shop. DAMHIKT! In my rig, I actually reused the circulating fan from one of the units.

I can't over emphasize this—you must put a good suction filter between these compressors and your appliance. Dust will kill them very quickly as it will gel the lubrication oil. Finally, I exhaust them into a condensing coil with a drip cup to recover any oil mist. I also give them a drink of a tablespoon of compressor oil after every 2-3 hours of use.