Cecil - I never built one of these do-it yourself units; just heard about it. Since it is pretty cheap, a backup compressor would be a real good idea. I would think the electric motor would be pretty dependable and may not need a backup.
I'm not sure of the psi or cfm produced. I may check into this idea this summer with a car mechanic. I'm sure the air conditioner compressor has specs to give one an idea of what it can produce.
