The problem with these air conditioners may be the fan not running at the proper speed.With the car running and the air on ,wet the condensor with water see if the air blows colder.If the condensor gets hot then the high pressure will rise causing the compressor toengauge and disengauge.This may not be your problembut only takes a minute to try.I am a forklift mechanic and we have lifttrucks with air and very commonly the fan will run and seem ok but will actually not run fast enough to cool the condinsor.