A.c. compressor

Your high and low pressure readings will vary due to ambient temperature. Mastercool has a download chart so there is no guesswork. You will need a manifold set to do this properly. They can be rented sometimes or just buy one. I suspect you might have more than one issue due to the age of the vehicle such as a leak, clog, and most likely low on freon. Not a big fan of leak dye but sometimes it's necessary to pinpoint a problem. On older compressors a common issue is that the center shaft O-ring develops a leak which can be tough to diagnose if it's in a early stage of failure. On many fords there also is an inline filter called an oriface tube that can get clogged up over time. This would require capturing the freon and pumping down with a suitable vacuum pump. Other items to replace during this time is the receiver drier. If there is a leak and you don't find it you will be back in there again. Good Luck!