I have a buddy who has offered me an old air conditioning pump that he is using for a door stop. It looks to be in good condition but I have no clue what it came off of or anything else about it. My question is what should I look for on this AC pump to turn it into an onboard air compressor to fit on my Power Wagon? And what is involved in this conversion? I would love to here the sound of my impact wrench in the middle of nowhere.
Any ideas?

Normally the R134 or R12 coolant in the a/c unit will keep it oiled. Since you won't be using that, you will have to add a pre-oiler before and then a oil separator after the unit.

You can also find converted a/c units that have greasable bearings and such to use instead.

I setup my onboard air with an AC compressor. I posted some pics and diagram here. It is very straight forward and it came out as an awesome setup. Definitely usefull for powertools on the trail or garage:

http://www.geocities.com/guieberhard/jeep/jeeprenegadeair.html

here is a diagram I developed on top of Jon's previous setup:

http://www.geocities.com/guieberhard/jeep/diagram_onboardair_carb.jpg

Hey thanks alot, those web pages help out alot, It looks like on your setup you have a preoiler, where do you get one? And how does the oil stay out of the air lines?