A/C compressor does'nt start

I was wondering if someone could tell me how low the pressure would have to be to prevent the compressor from coming on a 1997 intrepid? I had my A/C completely rebuilt last year with the exception of the condenser, which as luck would have it failed this year. After having it replace I had a friend charge it and all seemed fine for almost a month, but now nothing. I still have pressure on both the low and high side but the compressor will not engage. As for the amount of pressure I couldn’t tell you. Here in Canada it's a real pain in the ass to get these things filled as they still treat R134a as if it is a major hazard to our environment. If someone could tell me how to bypass the low-pressure switch it would confirm if it were the problem, then I will figure out how to seal the leak and have him re-charge it again

Thanks