Plasma Machine

I have a Snap On YA 2001 which is a Century 2040 machine. I need a manual or wiring schematic for this machine. I bought it non working and figured out it has a pressure switch which acts as a safety not allowing the main arc to initiate unless it sees a minimum amount of air pressure. I jumped the pressure switch and I got the machine to cut. It works on high 40 amp setting but when I switch it to 20 amp or low it will only cut as long as the pilot arc is active. As soon as the pilot arc drops out the main arc stops too. I figure the main relay is dropping out but a schematic would be most helpful in determining why. Any suggestions will be appreciated. Regards to all.