A/C compresor diode?
 

Hi,

My 924S had no A/C originally, but I retrofitted one from an 1984 944. According to the wiring diagrams there is a diode at the compressor, but this was not among the parts I got from the donor car. A part number I cannot find in the catalogs either. Could somebody please tell me, where this diode is, how it looks like, maybe with a picture, and if someone has one or sale that is also interesting. Thanks!

No biggie here. You can pick up any 3 watt diode from Radio Shack. The diode goes across the a/c compressor leads. The purpose of the diode is to control the DC power and only allow it to flow one way. It keeps power from flowing back to the car should the grounds come loose. There is only one correct placement of the diode. One way the clutch will engage, the other nothing. The striped end of the diode goes to ground.

Hi wrench1,
Thanks for the info. The purpose of the diode is clear to me, however my compressor has only one lead, the plus. Minus is the compressor body itself. Thus I have a red/green cable leading from the plus lead to the supposed diode. This cable is marked on the wiring diagram as well. As in that area of the car things are getting wet and dirty, I though to look for a matching diode in some tight housing :) Anyways, thanks for the info, I'll see what I can pick up here in Germany :)

I typed out a whole post saying you didn't need that diode but I realised I'm wrong on that. When you shut the compressor off, or if the clutch gets stuck somehow, the electromagnet coil that operates the clutch could possibly turn into a generator since its a moving coil in a possible magnetic field. So you'd get voltage backfeeding the system possibly in a worst case scenario. So yeah you'll need to source a diode for that to be 100% safe.

The clutch could even get stuck on by generating a self reinforcing field kind of the way the alternator works without any magnets in it.

I could see if there is any diode on the ac compressor I have, its got bad seals anyway. There might not be one since this came off a 944 as well. If there is I would just give it to you for the price of shipping, or ship cash on delivery if they still let you do that. I'll check and see.

Wow, this reasoning is solid, never thought of it that way! I was also convinced that this diode makes no sense, but it certainly does, as you say.
Thanks much in advance for checking! Am looking forward to it :)

No problem. We got six inches of snow last night so I'll try to check later today if I can. Got to find out about a shipping rate for someone else unrelated also if I can so if I don't get to it today I'll try as soon as I can.

Sounds good, thanks! We also got some snow, but not more than an inch or two...

Sorry man, no diode on this compressor, just the magnet coil and wire unfortunately.

Alright, thanks for checking though!

I have a spare A/C compressor from a 1983 944. I could go look for this diode

I would appreciate it!

I know it's too late (old thread) but for anyone looking for the diode it is a 1/4 inch square plastic piece over 2" long that mounts on the 12volt feed line about 9" from the compressor. Has male and female spade connectors in the ends. I just found mine came unplugged at one end.
part #944 617 108

???

Not near my AC compressors or wiring.
Might be a Canada BC Option

http://forums.pelicanparts.com/uploa...1379337549.jpg

J_AZ

Possible I guess. I took the part number from my parts car as it was easier to get at but both cars have it in the same spot.

I double checked the runner and what I took to be a diode (looks a lot like the diode off parts car) is NOT a diode. It may be a kind of inline fuse. It is on a short wire at the top of the left side mount and I can not see it well enough to find any markings.

This is what is on my Compressor 12V wire:

http://forums.pelicanparts.com/uploa...1379375037.jpg

J_AZ

Hi all, I got a diode from a spare car, it's yet not built in, thus can put here a picture if anyone interested. It's indeed a small plastic thing with male and female connections, just as if it was meant to connect to cables. Cheers.

Here is the diode I was describing. You can see the symbol on it. Sorry for the quality,had trouble setting the camera for close up.http://forums.pelicanparts.com/uploa...1379996204.jpg

That's how mine looks like too.