Wiring the a/c compressor (Puter?)

[grtskydog]

I'm doing some under-hood wiring repair/consolidation. On the a/c compressor there is the 2-terminal plug with 3 wires that go to a diode...and that's as far as I get before I get confused. On the diode, you have a black wire coming out the top AND the bottom, plus the black/yellow hash coming out the bottom also. I'm sure the bk/y-h is the 12v and the 2 blacks are grounds. I'm just confused as to how the diode is wired the way the factory did it and-- if one were rewiring stuff--if there's a better way. Could I just run a ground wire and then put a automotive diode on the bk/y-h wire only? I don't run a "kicker" solenoid on the carb anymore, and I'm not tampering with the wiring on the drier/accumulator. Just the portion that "triggers" the compressor.

Any thoughts? Thank you in advance for sparing me any dissertations on altering the way the factory wired it 'cause "Ford knows best."

[grtskydog]

LOL!! No takers? I was looking at the 1985 Wiring PDF and it looks like the diode is wired on the ground side. Looks like they are just trying to make sure the current doesn't flow back thru the compressor clutch...although I don't really see how it could anyway. The stock diode on my car is damaged and the wiring is shot, so I need to figure this out.

[bob85gt]

about 15 years ago my factory diode quit working. came to the same conclusion that it is to stop back feed. went to radio shack bought a big diode and has been running since.

[grtskydog]

Did you put the diode on the hot side or ground side? Thanks.

[bigjason_5]

The diode is for a voltage spike. When the compressor is shut off, the coil windings produce a huge voltage spike, which can damage computers. I would leave it alone, but if you must, you can use a different one. As long as it's wired the same way it will be fine. If you wire it backward, the compressor won't turn on at all. If you're just trying to clean up your engine compartment, you can use the diode that's already there and just move it, using longer wires. Would that possibly accomplish what you're trying to do?

[grtskydog]

Well, my situation is similar to bob's. The stock diode is kinda f-ed up, so I was just going to replace the diode. The stock diode is kinda weird, cause both ground and power wires run into it and I'm not sure how to wire a replacement.

If it's for spikes, then it would make sense to wire it into the power side (in the correct direction, of course) so the spike doesn't flow back into the system.

[JACook]

As bigjason_5 says, it's wired across the compressor clutch coil to prevent Voltage
spikes when the compressor clutch is de-energized. In electronic terms, it's what's
known as a "snubber".

Whenever you switch inductive loads on and off, the residual magnetic field creates
a Voltage that is opposite polarity from the Voltage that was originally applied to
the load. This is how transformers (such as ignition coils) work. The opposite polarity
Voltage spike can damage driver transistors, or when a relay is used, it erodes the
contacts, and in some cases, can literally tack weld the contacts together. It is
also a significant source of electrical interference, which is most likely why Ford
would put it there on injected cars, but not on carbureted ones.

The diode is wired such that it has no effect on the normal polarity voltage that
energizes the compressor clutch, but presents a direct short-circuit to the reverse
polarity Voltage spike when the clutch is de-energized. Connect the anode (+) to
ground, and the cathode (-) to the voltage side of the clutch coil.

[grtskydog]

Thanks Jeff. That explains why both +/- wires go into the diode.

[Puter]

Sorry for not seeing this earlier, I was out of town busy. Seems that you got your answer.