I'm contemplating salvaging a used refrigerator compressor to use to aerate my pond. A new compressor actually intended for pond aeration is 600 to 900 bucks.
There are several good youtube videos on repurposing old compressors for DIY air compressors for low demand usage, and I know someone who used a reefer comp and a water tank to power the air stapler he used to build 300 bee hives. In that usage it was running 8 hours a day for several months.
More info: Checking a few replacement compressors at random they have a displacement of 7 to 12 cubic centimeters. If run at 1800 rpm, and using 10 cm^3 for the sake of round numbers, we get 18 liters a minute, or not quite 5 gpm. If perfectly efficient, this works out to about 17 watts.
Oil lubed air compressors typically put in about 1 mg/m^3, or about a mg/hour. 24 mg/day, about 0.6 g/month. Bacteria will eat oil. This may well be within the munch capacity. However oil separation filters are cheap, and will handle any aerosols. Not sure if oil vapour is a concern.
I have found that temperature is a concern. If I need to use an oil/water separator, I have to keep it from freezing. Given winter temperatures of potentially -40, this probably means keeping the compressor inside the house, or at keeping the trap inside the house.
Questions I don't know:
Will the compressor survive a 100% duty cycle?
How do I check the oil level -- it's no longer a closed system.
Fridge compressors typically have an output at about 120 psi. My pond is 14 feet deep so will take ~7 psi. Will operating so far under design be harmful?
Should I be asking this on Engineering.SE instead?