with the system in a low pressure state the compressor will likely not turn on... there was more than likely a leak somewhere for it to have no pressure at the shrader valve at all. cheapest way to get going is to try to fill it and see if it works. Negative impact is, if there's any moisture that got into the system, when you try to charge it youll more than likely blow the compressor shortly after. You need to get the dye and do a UV test to find if it's leaking. Do you see any green oil around the compressor at all?