York for cheap on ebay.

Check out this compressor. I would get it but I already have one.

http://cgi.ebay.com/ebaymotors/York-Air-compressor-Air-Brakes-Semi-Pump-Belt-Drive_W0QQitemZ8057762515QQcategoryZ42605QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

much more worth it to buy a new one, you never know what tiype of condition those are in. just my 2 cents but eh

dont know about semis, but my dads dump truck's compressor runs all the time, they run the fuck out of those things.