A/C Driving me crazy

[Holidea]

Hey guys, got a 99 pathfinder 3.3. When I bought the truck the a/C worked gloriously but I realized that there was no compressor relay and someone had put a jumper wire in the relay spot. After removing the wire and buying a new relay, no compressor engagement. Anyone have any ideas?

[smj999smj]

There are a number of things that can cause the compressor to not engage, including low or excessively high refrigerant in the system, a bad thermistor (aka "thermal amp"), a wiring issue (shorted/open/excessive resistance) or even a bad ECM. A factory service manual will give you the step-by-step diagnostic steps to address an A/C compressor that will not turn "on," but you will also need a set of R-134a pressure gauges and probably a 12v test light and multimeter (and possibly a capable scantool). Jumping the relay is not a good idea, because it disables the systems ability to cycle, which could lead to excessively high pressures causing compressor damage and/or a hose to bust.