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O.T. Cherokee AC Clutch mystery

K

Kevin (FL)

Member
1998 Cherokee, 4L engine. Symptoms: AC clutch "chattering" (but clutch not engaged) when AC turned on. All mechanical components are good. When 12v+ is applied to clutch wire, the clutch engages fine and the system functions properly. Swapped out Siemens AC clutch relay (under hood)with a known good unit, symptoms repeat--a loud "chattering" sound on AC clutch, but no rotation of compressor. System is not fully charged yet; readings 35PSI low side & about 160PSI on high side. Outside temp 78 degrees. Is there a clutch control module that I can replace or is this buried in the PCM? Thanks.
 
HI,
Hard to diagnose one without bein' there,
but check the gap on the clutch contacts.
Some are adjustable, and if too wide, could be rapidly engaging/disengaging due to gap bein' too wide.
Just a thought, nephew had one with a similar problem,
and that was it.
 

I spec you have a voltage drop to the clutch,,, check voltage while the clutch is in chatter mode,,, that is if it only chatters while switched on,,, check air gap,, if air gap and voltage OK probably a weak clutch coil,,, I have wired in a relay to power up the clutch,,, use the clutch wire to energise the relay use the relay to supply battery direct feed voltage to the clutch...

I have not had any problems with the late 90's jeeps,,, the early 90's and older had a problem with current lost
 
Hobo/dbernie,

We recently bought this vehicle and the existing compressor appeared to be a rebuilt unit. When the AC was running a noticeable vibration occurred which we lived with a couple months and then the clutch symptom appeared. At this point I made an incorrect assumption that the compressor was fried so I had the system evacuated, removed the existing & installed a new one (along with accumulator & orifice tube). So, with both compressors the clutch symptoms did not change....that's why I believe the problem is in the control circuit. Note that I also "hot-wired" the clutch for test purposes and the clutch and the AC system functions correctly.
 
You beat me to it. But I was gonna say run a wire to the clutch and bypass the control. I have seen wires that looked good on the outside. But were broken on the inside. Caused the voltage to change with vibration.
 
(quoted from post at 16:09:48 07/02/10) You beat me to it. But I was gonna say run a wire to the clutch and bypass the control. I have seen wires that looked good on the outside. But were broken on the inside. Caused the voltage to change with vibration.
Click to expand...

I would not bypass the control circuit,,, only use it to power up a relay to insure that battery voltage is supplied to the clutch.

KOEO a min of 12V to the clutch
KOER a min of 13V to the clutch,,, the more the better

KOEO 11.5 will not cut it
KOER any thang less than 13V will not cut it...

It would be nice to see battery voltage KOEO are KOER,,, it does not take much to pull in a replay that's why you can get by with the low voltage at the control side...

It would also be nice to know the AC clutch amp draw,,, I am think'n 3/4amps max,,, more and its gonna affect the voltage measurement....
 
How fast is the chatter? A rapid relay chatter is caused by a voltage drop on the coil power feed in the relay.

Bad connection somewhere.
 
Hobo,

The identical problem occurred with two different compressors--1st one that came with the car was rebuilt and the one I installed is brand new. Also, the clutch works perfectly when 12v+ is applied to the lead-in wire going to the clutch coil. The air gap on the new compressor on the '98 is less than 0.020".

Also, the thing that's so strange with this situation is that the clutch plate doesn't even move while all the racket and vibration is occurring. Next thing I plan to do is to see if I can detect any magnetism when the noise happens. And some follow-up info: Today I noticed when I inserted the AC clutch relay, the clutch engages, but only for a half-second or so. And when I connect a test light to the clutch (lead-in wire) it also lights up for an instant when I insert the AC clutch relay into its socket. Don't know if that provides any clues as to what's happening....??
 
Russel,

It sounds like steel ball bearings being poured onto a glass tabletop or maybe being shaken up inside a small can and it also causes a strong vibration on the engine. Again--the strange part is that I can connect 12v to the lead-in to the clutch and it works perfectly--no noise and no vibration. I'll try to get a voltage measurement at the lead-in connection while its going wacko...
 
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