I hooked up my new A/C hose that I just bought, and started putting free-on into the system, only after 1 can (14oz.) the system showed 35 pounds of pressure, after 2 cans it was up to 50 pounds of pressure. The A/C worked for a week, but then started blowing warm air. I checked the pressure and it read 100 pounds. When the engine was turned on,with the compressor on, the pressure dropped down to 70.

This isn't right is it? I thought that it's supposed to take 3 cans to fill this system, ('86 305 F TA) and then would only be around 40-45PSI.

 

Did you add refrigerant to an already semi-full system? You can't add R134 to R12 or your seals are going to get eaten (plus the switching is not right for 134). Also too much pressure will make your system run just as bad as too little pressure. Overpressurizing your AC system is not good.

 

did you evacuate the system? sounds like you have air in the system. you need to pull a vacuum to as close to 30" as you can.