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Old 07-20-2010, 03:19 PM
Dan Dan is offline
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'89 300CE A/C compressor clutch not engaging

Hi, having researched this from numerous very helpful posts, I appear to be at a bit of a dead end. Some details:

1. A/C did work even though it wasn't the coldest, R12 low probably. (Compressor replaced etc a few years back, only little use since.)

2. A/C recently stopped cooling, compressor not engaging.

3. With engine off, clutch disengaged, outer compressor wheel spins freely with no noise or resistance.

4. Aux cooling fan low speed resistor found toasted, awaiting replacement, but aux fan does work at high speed.

5. Shorted/bypassed low-pressure cutoff switch leads at dryer with engine and A/C on, can hear clutch 'click' but compressor still doesn't engage.

6. Connected +12v to compressor blu/grn wire and also can hear clutch 'click.'

Seems like controls to compressor clutch are working properly but clutch, despite click when energized, is slipping or not engaging? No evidence of excessive wear or oil leak (leaky 103 engine w/valve guide seals) on or near compressor.

Haven't checked clutch gap, assuming with relative newness it was OK.

I've seen a post about using brake fluid or Simple Green to clean clutch surfaces, then rinsed off. Where should this be applied?

Any thoughts suggestions appreciated...

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Old 07-20-2010, 06:33 PM
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Location: Evansville WI
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If the clutch is clicking but not engaging, then would just about have to be a bad or misadjusted clutch. No idea why this would be incorrect if it's only been used a little and the compressor was new a couple years ago. Although the clutch is sometimes not included with a compressor, so may be swapped from the original, which might explain why. Usually a shop would try to get the owner in to a new clutch at the same time. Did you own the car when the compressor was replaced and if so does this sound familiar?
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Old 07-21-2010, 10:50 AM
Dan Dan is offline
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Gilly, appreciate the comments. I went back to repair order and it did not indicate that compressor w/o clutch was purchased, so I am assuming it was complete with either a new or rebuilt clutch as well.

Yesterday after using some brake cleaner spray and a bit of banging on outer compressor wheel to free anything that could have been stuck, the clutch may indeed be engaging now. With A/C on it draws ~ 3amp to the compressor terminal, and w/o engine running and it energized, I cannot turn outer wheel by hand; it's locked (it's free with circuit open).

With engine and A/C on and low pressure switch bypassed, there is a slight cooling to air coming into cabin through vents, even though I cannot hear the compressor running. I'm used to compressors making some observable noise but perhaps it's masked by engine noise? (BTW, I earlier checked serp. belt tension and upped it a bit since it was somewhat low on tensioner arrow indicator.)

Could low refrigerant (R12) make the compressor run quiet?

I guess next step is to get system refrigerant topped off and go from there?
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Old 07-21-2010, 08:46 PM
Yak Yak is offline
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Location: San Antonio, TX
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I'd double check the clutch gap and electrical connections. I don't have the specs for your car, but the R4 compressor has a small gap of 0.5-1 mm. Mine was significantly more than that, but I had/have other A/C issues, too.

Maybe also check impedance of the magnet and current draw. 3 amps sounds a little low, but in the ball park. The specs I've seen for a few different compressor clutches are a bit higher. The 123 FSM specs the R4 at 3.9 amps cold/3.4 warm @ 13.5 volts. I measured the impedance at 3.7 ohms, and I've seen comparable numbers for healthy coils.

After I committed to a bunch of other repairs, I did notice that the connector had not been attached properly to the compressor. The factory spade connectors have a spring-like connector for a tight, locked-on fit. When I looked at my connectors I noticed they were polished/burnished on the outside from a friction fit against between the compressor spade and plastic housing. I ended up sliding the wires out of the plastic housing, using needle nose pliers to get the spade fitting on right, then sliding the housing over the wires again.

You're probably on the right track with getting the electricals correct, then checking the charge.
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Old 07-21-2010, 10:09 PM
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You should have verified you have enough refrigerant first...not as a side question. Get that figured out then let us know.
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Old 07-22-2010, 10:35 AM
Dan Dan is offline
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Good point! I suspected so and confirmed it when low pressure switch activated and cut out compressor. All I have is sight glass -- no gauges - and there are just a very few bubbles. I'm hoping one can will do it.
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Old 07-23-2010, 12:06 AM
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Just as ps2cho has posted before your thread, remeber you must also rev the engine to 2000 rpms to pull in enough freon to have the low side pressure at enough pressure so as not have the a/c cutout at roadway speeds.

BTW ps2cho is the man on A/C hes had his dash out for pods and everything. He helped me and I thought I knew what all my issues were.

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