Steve,
My compressor is not coming on at all and I'm trying to troubleshoot the problem. At the low pressure switch, I get 12v at on side and 0v at the other (the switch is open). Does the switch need to be closed for the compressor to run? If so, is a low refrigerant charge a possiblity or is the pressure switch bad?

My initial thought was that even with a low charge, the compressor should come on and if the pressure is too low, it will shut off.

Thanks,
John