Wow! Thanks for all of the help guys.

Vara4-Kurt Yes, it has a small plastic air hose running from "tank pressure" to an air plunger that kicks on/off (?) the air pressure regulator electrical switch. But it looks more like a maximum pressure safety switch to me. I looked at it, and it is clean and has a small spring inside that looks like in a tire valve core.

RSpears - Rodger Yes, it blows the circuit within 20 seconds of when the compressor starts even with the tank line disconnected from the compressor head, ie: as in "no load".

Jerry, Possible but it's been working just fine for the past twenty years with the same things running off of the same line. I even run my MIller 130XP 110 volt mig welder on this circuit with no problems (I'm carefull to not have more than one heavy load on at a time, ie: only one tool, the table saw, welder or air compressor at a time). I did replace the circuit breaker which had to be more than twenty years old. The new one does the same thing.

Vara4-Kurt Yes, it has a low "on" at about 40# psi and a high pressure "turn off" at about 100# psi setting. I will have to do some more research about the pressure relief valve. It makes sense to me. Also, it a 110 volt system, not a 220 system.

Angrystroker I agree, that's why I pulled it all apart today to look it over. It's really a simple "oil less" system, just a rod and a bearing attached to the motor with a short crankshaft. It still blows the cicuit without any load on the compressor.

You really take your shop compressor for granted until it's broken. I'd like to know for sure what the exact fault is, before I start ordering parts because money is really tight right now.