Where is the low pressure air-conditioning service port on a 1994 Pontiac Grand Am?

The low pressure port of the A/C system usually has a blue or black dust cap and is located either on the larger diameter metal tubing typically found between the evaporator and compressor, on the compressor itself, or on the receiver drier (orifice tube systems only). The high pressure service port is found either on the smaller diameter tubing or the compressor and is larger in diameter. Only charge through the low pressure port. There is a web site with a lot of help full information about your auto a/c system check out the link below.