I can't seem to activate my A/C clutch. When I turn on the switch with engine idling, there is a slight increase in RPM, which is normal, and indicates the switch is working. I tested the relay (switched with the horn relay) and it is working fine. The 10A fuse is not blown. Would the A/C diode 'fuse' cause this problem? I wouldn't think so. I don't know how to test the diode, but I found it doesn't have continuity, which I suspect is normal. Anyone know how to check the diode? If the diode is OK, are there any other things to check before testing the clutch itself? What is the best way to test the clutch? -- Dana In terms of timetables, as quickly as possible-whatever that means."-On the president's time frame for shoring up Social Security, Washington D.C., March 16, 2005
The diode is just to protect the electronics from the 'inductive kick' of turning off the clutch electromagnet. Many digital voltmeters have a diode test function but with most simple ohmmeters, the diode may test open. Biggest problem is if the diode is shorted. (diodes are supposed to pass current in one direction only) Pull the connector at the clutch and test with an ohmmeter for continuity first. Should be something like 10 Ohms (just off the top of my head). If there is no continuity, the coil is open and the clutch needs to be replaced. If there is continuity, get some jumper leads and ground one side of the clutch coil. Connect the other lead to battery+. (engine is off for this test). Clutch should activate and pull in the armature. If the clutch still does not activate, the gap between armature and stator is too much and the clutch needs to be replaced. If it does pull in, check further back in the electronics. Hope this helps. Oppie (2001 LW300) ps - I have the 00-01 shop manual if you need any diagrams.
Thanks! Next question, could there be something else locking it out - for instance, the ambient temperature switch malfunctioning or the switch that disengages the clutch on hard acceleration, or is that all done by the ECM?
The most common cause of this symptom is low refrigerant. The AC compressor is protected by a low pressure cutout switch which prevents the clutch from activating if the pressure is too low so that the unit does not self destruct by running without sufficient refrigerant. I do not know about this model Saturn, but many times you can pull the pressure cutout switch connector and jumper across the contacts and then see if the clutch engages. If it does, then do not run it more than a few seconds. It means the system is leaking or (less probable) that the switch is bad. Good luck and report what you learn for others to benefit. Bob
True, Low refrigerant pressure can cause the evaporator to ice up (or worse) so there is protection for low gas pressure. There should also be either a superheat sensor or an ambient temperature sense somewhere that will shut down the compressor below a certain temperature to protect it. Low ambient temperatures might cause liquid refrigerant to be returned to the compressor. That both dilutes the oil in the compressor sump and can destroy the compressor if the liquid is pulled into the cylinders. (just like water ingestion will kill a running engine...you just can't compress a liquid). By design, the liquid refrigerant is supposed to all boil off into gas in the evaporator and return only gas to the compressor. Thankfully, my lw300 has been running well and I haven't gotten into the specifics of the sensors ..
