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Old 11-08-2000, 08:55 AM
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My a/c clutch engages only when I rev hard, and after a while, it will cut out.

Steve has suggested that it's a bad ground, so I have taken some voltage measurements.

Have measured the voltage from the positive terminal of the clutch, to the negative terminal (mounting bolts), and also using the intake manifold as a "real ground". Both yield about 12.9volts, with no significant differences. This is when the clutch is not engaged.

If I give the clutch a tap to make it engage or rev the engine hard to engage the clutch, the voltage will drop to just below 12volts, about 11.9volts.

Taking a reading between the mounting bolt and the intake manifold with the clutch engaged, also verifies that there's no voltage difference.

Hence, what can I conclude? A mechanically faulty pulley?

BTW, what kind of current (amperes) does the clutch draw? Is there a difference using the compressor body or the clutch mounting bolts as ground?


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Old 11-08-2000, 07:57 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
The air gap is too wide. I have seen this over and over again. The only proper fix is usually to install a new compressor.

When the clutch gap is too wide, it is from the crankshaft of the compressor sliding outward in most cases, not from wear. I'd bet this is your trouble. The gap should be .5mm or so...

Donnie Drummonds
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Old 11-09-2000, 10:02 AM
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gosh, replacing the compressor? but the compressor still cools perfectly fine when it engages...not to mention it sounds like a very expensive fix...

is there an "improper fix" for this?

Where is this air gap you're talking about?
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Old 11-09-2000, 12:07 PM
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Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,784
Your seeing no difference using the a/c mounting bolts and/or the manifold as ground is not a good ground test.
Take the reading from the a/c plug and use the battery neg. as the ground . If that reading is higher, your poor ground is the ground strap from the engine to the frame of the chassis.
[ usually down around the trans bell housing.]
That is what is meant by bad chassis/engine ground.
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Old 11-09-2000, 06:23 PM
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Join Date: May 1999
Location: Charlotte, NC, USA
Posts: 688
When asking questions concerning your car you should tell what it is. I assume you're talking about a Nippondenso AC unit.
If so, why do you have 12.9 volts at the compressor if it is not turned on? This doesn't make sense.

And if the gap is too large the compressor does not have to be replaced. It needs to be removed and put on a bench. There is a nut in the front of the clutch, remove it and the front hub. Under the hub, as it contacts the ridge on the shaft is a spacer that comes in different thicknesses. Find a thinner spacer and your hub is closer. Time consuming but not expensive if DIY.

Tobias MB
C280Sport, 300CE, 400E, 190/5.0
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