I have an a/c automobile compressor that I am attempting to use as a regular air compressor on my vehicle, mostly to inflate tires and have a compressed air supply for various uses(which is not a novel idea, you can find a lot of references and information on how to do this on the internet). I bought a standard 5 piston rotary a/c compressor that when turned uses a wobble plate to move the pistons. Because of space constraints the compressor has to run so that the pistons are pushing air towards the ground and the inlet and outlet ports are on the bottom of the compressor. Unfortunately, along with pushing the air towards the ground the PAG oil that is used in the compressor is being pulled down by gravity and subsequently is also being pushed out of the compressor by the cylinders. Initially, I tried to compensate for this by having a hose connected to the outlet port running upwards and rising higher than the compressor itself, that way, I thought that gravity on the oil that was pushed into the hose would hold back the rest of the oil in the compressor (similar to a manometer). However, the compressed air coming out of the compressor pushed all of the oil all the way up the 1 foot hose and into the filter bowl of the filter connected to the hose.
I believe that I can solve this problem by increasing the viscosity of the oil. That way the oil won't be fast enough from one piston compression to the next to fall into the piston cylinders and be pushed out. So I have done hours and hours of research and still am feeling uncertain about how best to thicken the PAG oil. My concerns are twofold. First, apart from the fact that PAG oil is a Polyalkylene Glycol I am not sure of its chemical composition. I know that it has adverse reactions to chlorine but because the formula for PAG oil is a trademark secret there isn't much information on its chemical makeup. So I am not sure what it will react well to or adversly to if I do add a thickener. Second, I am currently thinking of using grease as the thickener to increase the viscosity. The greases that I am looking at have bases of Lithium, Aluminum, Clay, Elastomer, Calcium Sulfonate, and Sodium. The greases that I am considering the most are listed below, but how do I evaluate the reactions between the grease and any of its additives and the PAG oil. Should I avoid the use of greases with additives and stick to some pure thickener like pure silicone oil (is it even sold in its pure form intended to be used as a thickener?)?
1) Multipurpose Synthetic Grease - Silica thickened - (-20 deg F to +400 deg F)
2) High Temperature Synthetic Grease with PTFE - silica thickened w/ PTFE additive - (-40 deg F to +450 deg F)
3) Extreme Pressure Grease - thickened with PTFE and with moly - (-33 deg F to +400 deg F)

Any advice would be greatly greatly appreciated and thoroughly considered. Thanks, back2theFuture

Auto AC compressors use the LUBE to lube and cool the pistons in the compressor they are NOT ment to run dry that why a lube is put into them in the first place get a compressor off a truck or use 12 compressor i think you will have falures if run dry THOUGH if you can get the oil to seperates and return to inlet side on pump maybe will work. Also PAG is avalible in various vis grades BUT why even use it PAG was a replacement for use with the newer refrigerants that will NOT mix with the old style mineral lubes, just use a high vis mineral oil try a straight wt 30 or 40 motor oil
bruce