A/C Clutch Wiring

rwd_pete · Posted: Mon Jan 27, 2003 11:47 am Post subject: A/C Clutch Wiring

I'm just reassembling my '78 Malibu. It's been apart for 3 years getting refreshed, but should be back on the road this spring.
There were two wires going to the A/C clutch, one green & one black. The green one is connected back in the harness, but the black one is about 15" long and bare going away from the clutch. It's unclear in the wiring diagrams where this wire should go. Is it a local ground?
I was looking at some other A/C wiring that I had trying to understand it. It had a small connection between the wires at the clutch terminal, which from the wiring diagram appears to be a diode. My car didn't have one. Any idea why some cars have a diode here?
Any help would be appreciated.

Pete Birrell
'78 Malibu 350, 4speed

acauth1 · Posted: Mon Jan 27, 2003 12:58 pm Post subject:

The green wire is the clutch control circuit from the pressure switch. The black wire is common ground. The diode is to prevent a "spike" when the clutch coil field colapses.

87SS · Posted: Mon Jan 27, 2003 1:42 pm Post subject:

acauth1 · Posted: Mon Jan 27, 2003 2:03 pm Post subject:

Without getting too technical or verbose:
As current flows through the compressor clutch coil, from the green wire through the coil to ground a strong magnetic field builds up, and draws the clutch plate in. When the current is released, the collapse of this magnetic field induces a higher voltage "spike" in the opposite direction and can cause electrical component damage. Think of this as an ignition coil without secondary windings. The diode is there to dampen the spike.

rwd_pete · Posted: Mon Jan 27, 2003 2:47 pm Post subject: A/C Clutch

Thanks for the info. I think the black wire is long enough to make it to the battery lead ground connection on the alternator bracket. Even though it was 3 degrees F. this morning, coldest yet this winter, I want to be ready for the hot weather. LOL
BTW, nice website, well organized.

acauth1 · Posted: Mon Jan 27, 2003 3:08 pm Post subject:

Thanks!!