Questioni have a 2001 Hyundai Santa Fe, all fuses are ok. a/c was working fine, very cold air. all at once the clutch will not ingage.i put gauges on sys. and it has 97 PSI.is their a low pressure switch in sys. i see on high side.also replaced relay.
AnswerThe switch you see in the high side incorporates three switches in it; there is no low side switch. 97 PSI is in the range that the air conditioning should operate, but may indicate a small amount of overcharging which could cause poor (but not absence of) a/c performance.
First, check the basic things and narrow down whether this is an electrical issue.
-- Do the radiator and condensor fans run when you turn the a/c on? If not, the ECM is not attempting to turn on the compressor.
-- Do you get power at the compressor when the a/c is on? If so, the problem is with the compressor or clutch.
-- Is the a/c fuse in the underhood fuse box blown? If so, you'll need to investigate why. There could be a problem with the clutch coil (in which case the fuse will blow when the compressor is plugged in but not when unplugged), or there could be a short in the wiring.
-- Note that the a/c will not work if the ECM thinks the engine is overheating. I'm presuming this isn't the case here.
+How the system works:
When turned on, the a/c switch sends power to the ECM and the temperature sensor (thermistor) in the evaporator.
If the evaporator isn't too cold, the evaporator thermistor sends powewr to the triple switch you've already found.
If the a/c pressures are in the proper range, the triple switch then sends power to the ECM on both the yellow/orange (or yellow/black) and green (or grey) wires.
If the ECM sees all the proper conditions (power from a/c switch, power in two locations from triple switch, engine running, and engine not overheating), the ECM will ground the a/c relay, which should then apply power to the compressor coil, causing the compressor to turn.
