Have an 98 Grand Cherokee The a/c clutch solenoid is staying engaged and running down my battery. Does any one know if this is a ground seeking or power seeking circuit to activate the solenoid. I know a lead comes from the powertrain control module to the a/c compressor clutch relay, but don't have a diagram or schematic to follow. Is there a way to test the powertrain control module.
thanks for any help
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JEEPR did pass the time by typing:
Should be the same as my 93ZJ
When I pull the relay the solenoid de-energizes. I'm thinking there is a short somewhere or chaffed wire, supplying maybe a ground for the solenoid to energize.
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substituting relays does not rectify it two wire connector at compressor need to know if its a case ground on the solenoid
Initially it was but it is also doing it in the off selection, why?
I'm only guessing here, but maybe try pulling the wires off of your ac- heater controls to check if maybe your switch might be the problem? You really need a meter to check properly as to what is happening. Even a cheapo 12V will work fine. The fact that when you pull the relay wires and the solenoid goes off tells me the problem is farther up the line. Your low pressure switch will always be closed, unless you have a leak and have lost refrigerant.
JEEPR did pass the time by typing:
That is the only thing it could be apart from the AC being on or the setting being defrost.
The ECU provides a ground (transistor switched) to the relay. A short anywhere along that wire will energize the relay.
Next step would be to disconnect the battery, and disconnect the harness from the ecu then ohm out the line. Watch that center bolt for the ecu plug, it's only there to hold the plug in, not to suck it in. Don't try to make the plug go in by cranking on the bolt, you will crack the ECU. That and it only goes hand tight, like a screw into plastic.
In the meanwhile if you don't want it running you can simply yank the relay. Pulling the high/low pressure switches (either one) will set a fault code but will also shut off the relay by removing the power feed. A short in the ECU output to that AC relay won't hurt the ECU.
JEEPR did pass the time by typing:
Let's back up one step.. do you have automatic climate control? If so then there are some other tests you can run to figure out what's going on.
Doug no auto climate control what does defrost have to do with the ac compressor
ECU? what is that?
That's what I kind of thought, would that be close to the powertrain control module that I had indicated in original post as it is a 98 grand cherokee
4.0Lwould that be close to (same as) the powertrain control
JEEPR did pass the time by typing:
In defrost mode the AC also runs even if the little lamp doesn't turn on. Heat drives away the humidity and the AC turns the humidity into water so it can drain out of the cab.
JEEPR did pass the time by typing:
ECU == PCM Different name for the same thing.
Should be on the firewall behind the coolant overflow bottle on the passenger side. Least that's where it is in the 93ZJ
Just so we all understand the solenoid is being energized even when the ignition is off. That is the cause of the run down battery.
OK done some reverse engineering the coil of the relay has a switched controlled ground and a 12v power supply controlled through ignition sw I guessing as the 12v is not constant the common contact on the relay has a constant 12v. for the clutch solenoid to energize with ignition off, a ground would have to be supplied to the relay and also a power source to energize the relay. So theoretically if the ignition switch was not shutting off all the way when key is extracted and the control was left on defrost this would cause the problem as I had described. Not sure were the low pressure sw. plays in this theory though, is it ignition controlled? But I recall the solenoid engaging with the heater in off selection I'm pretty sure. If the PCM was having a melt down you think I would notice more symptoms on other systems. Ok I think I just talked myself out of understanding what the hell is going on.
x1=12v sw x2= gnd sw C= common 12v constant nc= normally closed to common no= normally open or closed to common when relay is energized | or __ = contacts
-- | x2 | nc | x1
__no
__C
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