I have a few issues with the idea of using A/C compressors as high duty cycle air source for a pneumatic engraver. Such compressors are meant to remain hermetically sealed and use the flow of refrigerant directly over the motor to remove waste heat from within the compressor via the condensing coil of the system. Eliminating the refrigerant from the cycle eliminates the cooling for the motor. Secondly, simply strapping a axial fan onto the compressor shell as you have done will not provide sufficient cooling to keep the motor in good health unless your duty cycle is minimal. While the shell may feel cool when using such a fan to cool the compressor, inside the shell the motor itself can still be overheating and degrading the insulation on the motor windings. The motor itself does not have good heat transfer pathway thru the shell due to large spaces between the motor and the shell. It is also possible that such windings are already partially damaged if a used compressor was operated with contaminated refrigerant in the past.. There is a reason why these end up as scrap... And finally basic physics says that it is not possible that such a fan installed on the shell of the compressor can keep the compressor "colder than room temperature". Room air is the cooling medium... ergo the shell can not be lower than that without additional energy put into the system to extract the waste heat. I'd love to see an update on this
