Help. This old '79 hasn't had a/c working for several years. I have decided to change that for my sweet daughter, or try to. I have put a newer used York compressor on, with the proper PAG oil for R-134 in it, new O-rings all over, new dryer/receiver, new expansion valve. Hoses seemed fine. Hooked the single lead black wire from the compressor clutch to the green lead. I turned the thermostat/rheostat switch on with the the fan on and began trying to charge the system. The compressor clutch still would not kick in and so would not pull any more coolant from the can and obviously will not cool. Is there a low pressure switch on the '79? Where is it? Do I likely need to replace the evaporator? My rheostat switch only has one wire lead (green) going from it, should there be another wire from it? Remember it is a '79. How do I check for leaks? Please help? I feel like there is something basic I am missing. I think I may also need a new alternator that give strong charge in case you think that may be related. Help, I am feeling pretty defeated, and hot.