1996 850T 2.3 A/C and wiring issues

noll55 · Post by **noll55** » 12 Jun 2015, 14:37

I have a 1996 Volvo 850 Turbo with 180k miles. We've put a lot into the car the last few years, both on our own and via a trusted mechanic. While my mechanic was doing a road test the other day, he started to smell electrical smoke. 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? 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! Please tell me this isn't the end of our beloved wagon.

Post by **Ozark Lee** » 12 Jun 2015, 15:36

Are you sure the wires that are melted are to the high pressure switch or are they to the fan? I have never encountered melted wires to the high pressure switch and it would be unusual. Those leads go to the ECU and aren't really tied to the battery. If you could snap a picture of the melted wires and post it back 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.

Was the ignition switch a known problem prior to this?

...Lee

noll55 · Post by **noll55** » 12 Jun 2015, 21:42

Thank you very much for your reply! Sure. I'll attempt to include some pictures.

If they post, "wire 1" shows the small section of blue wire that remains after we cut the melted section away. I'm not sure if that helps any, but thought I'd point it out just in case.

Yes...the ignition switch was a known issue beforehand. We'd have rotate our key back slightly after starting the car to get the lights to come on and the gear shift to disengage. We did not experience any other problems or inconveniences, however.

Post by **Ozark Lee** » 13 Jun 2015, 00:23

Ahh, the low pressure switch. That one does have battery voltage through it. Those wires used to be Blue/Gray and Gray. The Blue/Gray wire comes from the A/C relay that is located more or less behind the glove box and the Gray wire goes on to the A/C compressor.

Your real problems are in the wiring harness that is shown in the 2nd picture. When the A/C wires melted they also melted the insulation on some of the other wires in that harness and no doubt they caused those other wires to short out. It is a real PITA but what you are going to need to do is split the wire loom open and start pulling each of the wires apart so as to look for other damaged wires - one by one. You will need to inspect and repair the wires in the harness as necessary all the way from the A/C relay to the compressor and that harness runs under the ECU box. There are many very important wires in that harness. At some point you will need to figure out what happened to cause the short in the first place. It could be the A/C compressor itself but my guess is that the wire to the compressor got its insulation skinned off and the short will be in the wire rather than the actual compressor.

Under the hood it shouldn't be all that bad but once it goes through the firewall into the cabin it is very difficult to get to without removing the dashboard. Removing the dashboard is a big job but it isn't really all that difficult. We have a writeup on replacing the evaporator core in the repair database that details the dash removal process step by step. Sadly you will likely also encounter broken dashboard mounts that will also need to be addressed but there are various methods for making the dash repairs in the repair database as well.

The repair time here is measured in days, depending on how much time you can dedicate to it it may extend on to weeks. This won't be a simple two or three hour fix.

...Lee

Post by **abscate** » 13 Jun 2015, 03:26

W hole you have that dash removed, think seriously about replacing the evap core. The part isn't that expensive, the labour is 1200 usd at a shop.

noll55 · Post by **noll55** » 15 Jun 2015, 08:44

Thanks, guys. I appreciate the replies. I'll let you know how it goes.

noll55 · Post by **noll55** » 15 Jun 2015, 16:18

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 was 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.

Post by **Ozark Lee** » 15 Jun 2015, 16:27

That harness is pretty charred back beyond where the leads come out to the pressure sensor and I don't think you will have much success with just changing out the ignition switch. My guess is that you have multiple shorts back in the harness and the only way to clear that up is to split the loom and deal with the burned wires one at a time. It isn't terribly difficult but it is laborious.

...Lee

noll55 · Post by **noll55** » 15 Jun 2015, 17:10

Crap. I will tow it back to the house and check the loom and maybe pull the dash, but...I'm guessing I have a car to sell.

Thanks, Lee. Appreciate the reply. Again...I'll let you know what happens.