This is not my suggestion it is one that I read in another forum and I thought it was well written and made good common sense.
Let me add a tip to this old thread, the best way to know how many hours as you compressor already worked (for example to control oil changes and such) is to put an industrial type hour meter between the pressure switch and the compressor electrical motor. If you wire it this way the hour meter will count only the time that the compressor is really working. This type of hour meters is quite used in many industries to control service time in machines including air compressors. And there some of this metters that sell for quite cheap (chinese crap...)
I'm not sure how to exactly wire this up but it sounds like its worth doing.
