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compressor slugging?

mhamilton on Sun June 27, 2010 1:31 PM User is offlineView users profile

Year: 2000
Make: Cadillac
Model: Eldo

I had to replace my original compressor because it was leaking out of the case. A previous owner/mechanic had put in green UV dye, and it was enough of leak to cover the compressor in green oil (though the system was still charged enough to run, but didn't cool well).

So, I put in a new Valeo compressor, checked the orifice and found it clean (replaced with new anyway). Recharged by weight and it's been cooling just fine since. The problem is, after the car sits for more than one day, as soon as the compressor engages the 1st time I hear a loud "crunch" sound. Never does this after, only when the car hasn't been run in 2 or more days. Never made this noise with the old compressor, and doesn't happen when it cycles or if I stop and restart the car the same day.

Is this slugging? My only guess is that this is due to oil? I have no idea how much oil was added to the system with the UV stuff. I did put about 2 oz in the new compressor, spun it by hand, and drained most of that back out. Then put in 1 oz and installed the compressor.

Is there anything I can do, short of starting all over and flushing out everything?

Thanks,
-Michael

bohica2xo on Sun June 27, 2010 2:46 PM User is offline

Let the car stand for 2 or 3 days. Turn the compressor shaft a half dozen revolutions by hand before starting.

If no "crunch", then you know the answer.

B.

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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

mhamilton on Sun June 27, 2010 3:30 PM User is offlineView users profile

So it could be too much oil slugging the compressor? I didn't realize that was possible.

Does the HD6 hold a lot of oil internally? When I got the new comp, it seemed dry, so I assumed the oil that I put in to flush it came back out.

bohica2xo on Sun June 27, 2010 4:24 PM User is offline

With a low mount compressor & way too much oil it is possible. A long suction line with a good, thick (cold) oil film after a long run could drain to the compressor over time to cause an issue.

I suppose it could just be compressor stiction after sitting, and the clutch is actually making the noise. Turning a cold compressor by hand should reveal that as well. If it has significant breakaway when you turn it, then retest a few days later with a helper - while you observe the compressor under startup.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

mhamilton on Sun June 27, 2010 5:28 PM User is offlineView users profile

Thanks, that's a good idea, I'll check that. The only other thing I could think of was because I didn't do any burnishing of the clutch on this new compressor, didn't see mention of that in the service manual.

I swear, nothing on this car's ac system goes right. First time charging, the high pressure hose connector blows off, loose oil and refrigerant, have to start again. After that it turned into a leaking compressor case, so had to do it all another time.

Edited: Sun June 27, 2010 at 5:29 PM by mhamilton

ice-n-tropics on Sun June 27, 2010 5:57 PM User is offline

It's a good idea to burnish with 100+ engagements to overcome the starting torque caused by the static "stiction " of a tight new compressor.
hotrodac

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Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
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