Postby smj999smj » Wed Jun 20, 2018 8:48 am
It may be neither! If the refrigerant is leaking and has gone too low, the pressure switch will keep the clutch from engaging. A bad thermistor (sometimes called a thermal amp), which is attached to the face of the AC evaporator core, can also interrupt power to the clutch, among other things. The system needs to be properly diagnosed; the first thing that should be done is a set of gauges should be installed to check the system pressures. With the compressor not running, the static pressure should be around ambient temperature and a full system usually shows at least 70 PSI on both high and low sides. Of course, with the clutch engaged, these pressures will change drastically if the compressor is good. Low side will operate around 40-45 PSI and high side, which can vary depending on a number of variables including temperature and humidity, can operate in PSI from the high 100's to low-to-mid 300's. An AC performance test is listed in the factory service manual which takes into account these variables and gives specifications as to what the pressure range should be.
Another thing you can do to test the clutch and part of the system (temporarily) is run 12v of power to the clutch harness connector. If the clutch is good, it should engage and turn the compressor shaft. Keep in mind that the system should not be left like this, as this bypasses the protection systems in place to prevent damage to the compressor by shutting it off when the pressures get to high or too low.