[forest_grump]

Most have a low-pressure switch that won't allow a/c compressor clutch to engage when you are low on freon and sometimes will go bad....check that out first.........You do have fan (blower fan inside cab)on at same time right????? If inside blower fan is not on...it will not engage a/c clutch.Sorry gotta ask which fan lol...Might check for a/c relay in a relay box in engine compartment and listen to it for a click when someone hits on/off button inside with key and fan on) and if so check for voltage to a/c clutch on compressor...goodluck