Does anyone know where I can get a good wiring diagram to diagnose the AC system on a 93 945 (R134a)? The Volvo website doesn't have anything like it to buy.

The system works fine, but the compressor always comes on the second you turn on the blower fan, regardless of where the "AC off" swith is. If the blower is in the on position when you start the car, it gets pretty rough - the compressor is engaged during startup, and cranking is especially hard.

I know it's not the MCC panel, because I replaced it. Seems like the next thing to do is try to get in there and see what's going on - I'm thinking perhaps there's a relay somewhere in connection with this that's gone bad. Just don't know where it is.

If anyone has had this experience too, I'd love to hear from them. I think it may be a unique wiring problem, perhaps?

Thanks for any suggestions.

I'm guessing that you checked the Volvo tech publication site. I'd be surprised if they didn't have a suitable manual.

It almost sounds as if like you said, there is a relay issue. Or perhaps someone previously did some creative wiring so that the A/C would work.

You should disconnect the wiring harness at the accumulator and see if the compressor still comes on. If it does, the problem is outside of the normal a/c circuit, and might be a result of someone doing some work to make the system operational. In other words, a hack job.
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chris herbst, near chicago

Chris,

Thanks for your advice. The harness goes into the low pressure switch on the accumulator, right? That definitely works, because I've had to short it in order to get the compressor going to suck in refrigerant before.

I want to try and find all the wiring that's between the control unit and the compressor - I've heard that there is a relay on some cars, and not on others. It's got to be something in the wiring, since I've tried two control units and they're both fine.

The volvo tech publication site showed general wiring diagrams as no longer available, so I guess I'm going to have to go by others' experiences!

I just got the elec. manual/wiring diagrams for my '94 940 from the Volvo tech publications site - about $40 with shipping. The usual very neat and thorough Volvo manual. It shows the AC wiring paths clearly. My scanner's gone south so I can't send you the page, but in my experience, the wiring book is the most useful manual of them all, and pays for itself over and over, so try to get one.
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Bob (81-244GL B21F, 83-244DL B23F, 94-940Sedan B230F)

Thanks to everybody for their advice. I'm a little miffed that the tech site seems to not work as well for me - in the drop-down list for 940 turbo, it only shows one year available - 91. Mine's a 93, so I guess if I look for a 93 n/a it should be about the same wiring, anyway. Just don't want to buy the wrong one!

The Volvo site just shows as being out of stock, rather than unavailable. I'd send em an email or give em a call to see when they'll get some more. In the meantime, I have the wiring diagrams for a 1991 744 non-turbo, which is very similar to your car. It'll get you started in the right direction, anyway.

One thing I would check first is to make sure nobody has fooled with the wiring, like Chris said. On my car, some mechanic decided it would be cheaper to BYPASS all the A/C safety stuff with a Radio Shack switch hooked DIRECTLY to the compressor. I talked to a Volvo guy here and he said that wasn't that uncommon! Anyways, check the relay tray for any extra relays. A listing of them should be in the FAQ; if not, I'll email you a list.

-Greg

Greg-

Thanks a million! This looks really comprehensive. I'm going to start working on it and I'll let everyone know what I find (if I'm successful!)

cheers,

Ben