So..I'm driving home in rush hour traffic in my '91 745T, wondering if the wildfires in Magnolia are getting closer to my house, when the AC quits. Pull over to the shoulder, jumper the compressor and I've got cold air again. Great, another electrical problem, but at least I'll be cool getting home. Wrong. Couple miles down the road and my radar detector starts making a weird squawk instead of it's usual beeps. Shut the damn thing off, not my day. Then the radio starts cutting out, and the tach starts going wonky (speedo's already crapped out; got a rebuilt coming). Pulled over and got under the hood, and I've got like 11 volts on the battery, with no improvement if I race the engine. So, the alternator's crapped out again and I've got to make it home on the battery. Off goes the AC. No telling how long the alternator's been out, so I don't know how much battery I've got left. Turns out I've got about 5 miles, in the damn stop n go traffic. Car starts running like crap, missing out, no power, and all the warning lights are coming on, ABS, SRS, everything. Then I remember my portable jump starter/air compressor, which everyone should carry. The minute I hook it up the car smooths out and everything is good again - for awhile. I have to play around with it, but eventually I manage to get the hood closed with the jump starter still hooked up although only with the safety catch. Sure glad I've got some room on top of the battery; I'll bet you couldn't do that with a front wheel drive car. I'll leave it to your imagination as to how much I enjoyed the 20 mile trip home with no AC in 98 degree heat, particularly the stretches where there's no place to pull over. Biting my nails down to a bloody stump wondering if the jumpstarter has enough juice to get me somewhere where I won't be mandatorily towed for obstructing traffic if the car quits. The last mile to my house is slightly uphill and I could only make 20 MPH. The car died for good, just as I pulled in the drive.

I had a spare alternator, only an 80 Amp instead of 100, but it fits and works, so everything is good, now that it's over. AC, radio, and everything work, just like before. What really pisses me off, though, is that the battery light never came on, until all the lights did. It's kind of clever how the car started shutting things down to save the battery. First the AC, then the radio, then the instruments. Engine ran as well as it could up until the end. I wish now that I had thought to check the voltage on the battery when it finally crapped out. The Cadillacs I used to work on in the mid 80's needed at least 10 volts for the computer to work. Anyhow..I always thought that when the alternator went the battery light would come on, so you could deal with it before the situation got critical. Clearly, this is not the case. If anybody has any theory as to why this didn't happen, I'd be interested in hearing it..

 

Yea, definitely a Volvo flaw! I have had it happen to me the same way a couple of times, and the BAT/ALT light never comes on while this should be its main function as a 'warning' light...

 

Fantastic story. I felt like I was reading a action novel. And I'm jealous that you have AC that the car shuts off when the battery drops to a certain level. On my cars, the radio was the first to go.

Would definitely like to have a battery signal when the alternator goes, it would only make sense.

 

On my 740 when the alt goes, all the warning lamps go on.

 

Well, as of now, the best I can come up with is that maybe the alternator was charging like one amp or so, just enough to keep the battery light from coming on, but not enough to do me any good. Next time I'm at the wreck yard I'll probably pick up another 100 amp alternator since that's what I'm supposed to have. When I change it out I may try starting it after I've got the belt off. At that point it should be putting out zero volts for sure and we'll see what happens then..

 

Well, I know I'm preaching to the choir...but if you can only add one auxiliary gauge in an rwd Volvo...it need to be a volt gauge...they don't lie. I've had too many issues over the years w/ excitor wires and circuits. With a manual transmission, odds are you will get the revs up enough for the alternator to self-excite. Autos...not so much. A volt gauge is your friend!