A/C coil question

I have been over my entire electrical system. New altenator new battery ,cleaned all grounds, replaced battery terminals. Checked to make sure that altenator is putting out.
At idle I have 13.9volts, when I engage the A/C the voltage will steadily drop until the gauge bottoms out and the check gauge light comes on. I unplugged the e-fan no change. Then I unplugged the clutch coil connection and voltage increases back to 13.9. I am almost certain that the clutch h coil is breaking down and going to ground creating an excessive draw. There is no change in engine speed, like the compressor has a bad bearing. Has anyone ever had this happen? Does this sound right? Thanks for your help.

No idea, but I can tell you the clutch is an easy fix. The assembly should be less than $100 for everything from the coil to the plate. Pay attention to the air gap.

Sounds like a shorted clutch but there is a diode in there that could be bad causing the power drain to ground also. Use an ohm meter to check the coil with it disconnected electrically. If it reads steady under about 8 ohms (wild guess on my part) and reads say 1-2 ohms I would say it is shorted inside. The ohms reading will spike to near zero at first on an old analog meter. Give it 3-4 seconds to stabiilize as the back emf stabilizes. I would expect to see about 8-20 ohms on a coil like that but I am not and EE.

Ecomike said:

Sounds like a shorted clutch but there is a diode in there that could be bad causing the power drain to ground also. Use an ohm meter to check the coil with it disconnected electrically. If it reads steady under about 8 ohms (wild guess on my part) and reads say 1-2 ohms I would say it is shorted inside. The ohms reading will spike to near zero at first on an old analog meter. Give it 3-4 seconds to stabiilize as the back emf stabilizes. I would expect to see about 8-20 ohms on a coil like that but I am not and EE.

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You're spot on mate.

When I saw this post I though I would get off my duff and do some tests.

I did the resistance test and Diode test on a used AC Compressor stowed away in my man cave.. Pics show the results.

Resistance Test. Meter set to the 200 Ohm scale.



Diode Test. Meter set to Diode test. I guess the Diode is okay. I checked it again with the leads reversed and got .009. It's not open or shorted.



Diode testing - from my Ideal 61-310 manual.