I have a 1996 Volvo 850 Turbo with 180k miles. We've put a lot into the car the last few years. While my mechanic was doing a road test the other day, he smelled electrical smoke and by the time he returned to the shop there was smoke coming out of the dashboard. Here's what we know: the a/c wasn't running when I took the car in; the wire harness for the a/c high pressure sensor is totally melted; the car will start but stalls within ten seconds of turning over...often when the fans kick on; some electrical components maintain power without the key (did I understand him correctly?). I know my ignition switch is faulty, but why would that melt wires for the a/c system? So...I have no idea what to do and my "all makes and models" mechanic doesn't feel up for the challenge. Any ideas? I need your HELP! I don't want to scrap my car!

 

Where are you located? Sounds like you need to find a new mechanic. You should be able to find wiring harnesses or connectors at a recycle yard but it will take time to sort out the extent of the damage and root cause. You should be able to find some online info or Youtube vids on replace the ignition switch, but I'd also suggest an elimination process - ie remove fuses, relays to see if something other than the switch was shorting to push all that current to the pressure sensor. If you are so inclined, you can download the 850s wiring diagram from volvowiringdiagrams.com to find wiring junctions involving the AC sensor's wires. I'd also consider having the alternator checked out - its quite possible the voltage regulator may have burnt a few diodes to allow way more than 14.5 volts into the system... (you should be able to buy a replacement for just the voltage regulator not the whole alternator - although that may be another yard part to consider). Good luck! My thought here is to research the problem as if you are going to fix on your own, then if you're not up for the task, at least you know what a shop would need to do to sort things out.

 

Thanks for the reply, MT.


To answer your question, I'm in Maryland. All the sudden, I'm hoping you are, too! Ha!


I'm going to try and post a few pictures for you, in the hopes that it helps. I'll try to show the wires, the location of the sensor/switch, etc. If the "wire 1" pic comes through, you'll be able to view the blue wire that is left after we cut the melted section away.


In another forum, I saw this and I wonder if it might help:


"The car dying when the fan kicks on is also a 'tell'. The fan is a very high current device and it is current protected through a fusible link. I don't know what size the link is but some 850s have actually burned after the fan shorted out so it must be pretty substantial amperage. A shorted out fan could explain everything."


Thoughts?

 

yep sounds like a good avenue to go down. The fan is relayed and will sink a lot of current, plus its tied into the AC computer so if the fan goes caput the AC will shut down. Curious if the car will run with the fan disconnected, the fan relay removed and the AC turned off. Sounds like the fan motor or relay totally shorted and pushed all that current down a ground line or signal line... Reminds me of a time a buddy's VW shorted and took out a bunch of wiring into his fuse box - had to find a replacement for the harness and fuse box (dealer did the work under warranty but he had to wait 3 weeks for a part to come in from Germany!)

 

UPDATE. I stopped by the garage on the way home, excited to present our "shorted-out fan" theory to my mechanic. He said he had already unplugged the fan relay and it didn't help keep the car running; that he didn't think my issue would be totally related to the fan. So, he showed me a little more of what was happening and I wanted to pass the info along.


- after hooking the battery back up, the snowflake light illuminates and the display shows all 8's
- within 15 seconds or so, the orange snowflake light turns off and the clock shows 12:00...nothing else
- inserting the key and turning the power on (without turning over the engine), the two lights related to the A/C flash in sync and there is power to all the lights, wipers, radio, etc.
- if you start the car, it will run for about 10 seconds until it stalls as the fan comes on
- (here's the fun part...wait for it...wait for it) if you turn the car off and remove the key, all the electronics still have power


So...seems to me I'm looking at an ignition switch issue. I can swap that out, but will that solve all my problems? Please tell me it will. Otherwise, I have a Volvo 850 for sale if you're anywhere near MD. I just don't think I'm good enough to figure out a mysterious short.

 

You may need to do a bit of a process of elimination here or you can do some additional connectivity testing to look for possible shorts in the wiring harness.

Check out volvowiringdiagrams.com or volvotips.com to get a sense of what wires feed into what. You may need to pull relays and the ECU to see what pins should be open to 12V or ground. If you have a multi-meter, you can disconnect the battery (pos and neg) and then see where you have a direct connections (ie check ohms from the positive connector (not the battery) to various pins/connectors on the relay box or key and then move onto the ECU. You can do this with the key off, then with the key on to see if all looks in order. As my 19 Y/O son would say, "its not difficult, just tedious"...

 

I love working on stuff like this, I admit it. It's a stretch, in my opinion, to try to fix this sort of thing over the internet, especially third person using a mechanic. What you need is an electrician. But I will try to give you some thoughts on it. Auto wiring has always been a hobby of mine.

It would be good for you to sit down and look at how the wiring diagram is organized. You might not understand it at all, but at least see where you'd need to look if you want to understand what somebody else sees. It's a little strange.

So, the 10 seconds thing is interesting. I don't have an immediate explanation. However: There's no reason why the fan needs to come on, and that is your first mistake, treating that like it needs to happen. You need to turn the A/C off.

The wires going to the compressor have melted, so you need to turn that off. Turning off the A/C and the A/C blower fan will stop power in that melted wiring. Fortunately, it's pretty obvious where at least one short is; that circuit goes to the a/c compressor, but it also goes back to the ECM. Both of those are really close to the melted spot (you're not dealign with long wires)

Your problem with power staying on with the key out is also a great clue. however, you need to describe exactly what stays on. Give a long long list.

finally, I have a question for you volvo experts; would the immobilizer shut this car off? Is that the engine problem? I don't have a car with that on it. If you have that, read about it and let us know if it could behave that way.

 

on the 850s the immobilizer is tied to the horn and lights and if set off will flash lights/horn and not allow the car to start. With that said, low system voltage can mess with the immobilizer so as a test noll55 should check system voltage with car off (12.5 or so at the battery) then start car (14V give or take depending on what load is on). If something is shorted it could be dropping the voltage until the car stalls or it could be the alternator is pushing too much voltage which may also trip off the car's ECU.

 

It certainly seems reasonable; low voltage could be the cause of the shutdown. Something could be turning on. If that something is the A/C compressor, then the user can control that, thank goodness. So hopefully he'll come back.

Hey O.P. Do you have a volt meter? Half of life's problems require a volt meter to solve.