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Dave Martindale

writes:

Yep, when I tap the compressor clutch with a stick or
rev the engine. I haven't tracked down that problem
yet. It could be burned contacts on the clutch relay
causing low voltage to the clutch coil or simply a
sticking clutch. Of course, loose connections could
be the culprit. The darn thing's schizo.

Check the clutch clearance (with a feeler gauge).

I had a Honda Civic whose AC worked fine most of the time, but which
quit when the outside temperature was hot and the AC had been running
for a while. It turns out that the clutch either had too much clearance
when it was new, or it had worn to the point where it was now out of
spec. When the clutch was cold, it would still pull in fine despite the
larger gap. But as it heats up, the copper wire resistance increased
enough to drop the clutch current just a bit, and now the magnetic field
wasn't enough to pull in the clutch once it was disengaged.

Replacing the spacer washer to bring the clearance back into the
specified range fixed the problem for the rest of the life of the car.

(Outside temperature matters in two ways: the clutch starts off hotter,
and gets less cooling from the air when it's hot outside. Plus when
it's hot, the compressor is running a larger percentage of the time to
keep the car cool, so the clutch is engaged more and the heat dissipated
by the clutch winding itself increases.)

Dave