Volvo 940 weird AC/Electrical issue

I have a curious issue with my 940 wagon. It involves the AC and I believe it is a weird electrical issue.

I had the car recently serviced and in the process had the AC system charged as it had lost coolant. I assumed that was the only issue with the AC, by the way. I took the car home and the AC worked fine.

The next day suddenly there was no cooling so I suspected there might have been a large leak in the system. But then the following day the AC started working again! Basically, it is on and off one day to the next. Yesterday it cooled. Today it did not. It has been like this, on and off, for a week now.

Here is an important clue. On the days that the system works normally I have full self-test dashboard lights illuminating when I turn on the key. Everything lights up normally and then they all go out normally. Life is good. On the days that the AC will not work (as in no cooling) only TWO of the self-test lamps illuminate, specifically the seatbelt lamp and the SRS lamp. Then the seatbelt lamp goes out but the SRS lamp says ON!

Note that while there is no cooling with the SRS lamp illuminating all other electrical devices appear to work (windows, heated seats, power seats, wipers, blower fan, radio, headlights, etc, etc.) I can find nothing electrical that does not work. Only the cooling (compressor?) does not work, as if one had turned off the AC switch. I assume that some relay controls whether AC is on or not and normally that relay is operated by the little AC button on the dash.

Interesting thing. One day last week, while I was driving along with the AC not working and the telltale SRS lamp illuminating the lamp suddenly went out (I had been driving only 10 minutes) and, presto, the AC began cooling normally. The system was fine for the rest of the day. But the next morning when I started the car, back to the problem of no complete self-test indicator lights and no AC and a lit SRS lamp again!

I’d like to have some idea that someone already knows about what might be happening based on these clues before I have any actual work done on the car to fix it. The place that serviced the car has no idea (without first tearing things apart).

I would start with standard electrical system tests.combined with a intensive visual inspection of all components,connectors,connections.You dont mention year or mileage,do you know if there is a Scan tool from Volvo that can look closer at your Volvo than a generic tool? These munufacture specific tools can help with diagnosis.I say either a Volvo specific independant who is very familar with your model.Or dealer because they can access factory technical assistance.

1993 940 wagon. About 175k miles at this point. I don’t know about scan tools but I’ll see what I can learn about that. Meantime I could attempt that visual inspection of connectors, etc. that you suggest. I did look at all fuses at one point and they all looked fine but that was as far as I went.

Probably a dead-end on the scan tool search,your car is to old,for the tools that have the “extra features” I was hoping for.

Next time your a/c isn’t working, try ‘wiggling’ the ignition switch slightly, turning the key slightly forward & back (not enough to turn it to start or turn it off) and see if it improves. If it does, bingo! you have a bad ignition switch. Otherwise, look for a corroded or loose connection on something common to the a/c and the systems that don’t ‘light up’ A schematic for your car will be invaluable for this.

I have a 940 sedan that does the same thing. I hadn’t noticed the lights on the dash but I’ll watch for it. I took it to the dealer and they said this is a common problem. There is a loose solder joint in the control panel (above the radio in the center console) that causes intermittent AC. They fixed it, or so they said, and it ran OK for while but its back. Now when it doesn’t work I bang on the dash and it comes back on. Sometimes for a few minutes and sometimes for a while. You don’t have to hit it hard. I just use a fist and hit it on the passenger side of the center console near the AC control panel. That usually gets it to work. I’m going to try and remove the panel and see if I can see where the problem might be. Or I may install a new switch.