Which line on a 1989 Ford Ranger do you install freon?

you dont ... you take the car to an airconditioning service department and get them to do it for you Low pressure side. To find the low pressure side, look at the compressor. Two lines come out of the compressor, the high side goes to the condenser, which is the cooling coil in front of the radiator. The OTHER line comming off the compressor is the low side. Follow it back to the firewall. Somewhere between the compressor and the firewall is the test port for the low pressure side. THAT'S where you install the refrigerant for all vehicles.