LP fill port is directly below the power steering reservoir (sp?)
The port up front is the high pressure port.
As a general rule, look at the tubing size it is connected to. The small tube size is high pressure, the larger tube size is low pressure. Same on a home air conditioner. The smaller carries high pressure gas out of the compressor to the condenser to be turned into a liquid. The larger carries gaseous refrigerant from the evaporator inside the car at a low pressure to the compressor.