I searched. Honest.

'94 850t, ECC system, fan not working on any setting

I checked the fuses first. Number 31 was blown, # 5 wasn't. I replaced #31 and still nothing worked. I pulled the fan, hooked it to 12v, and it works fine.

So I did a bunch of searches, and ultimately went the easy route....swap parts with my other car. I've got a '95 with heat that works, and it's the same ECC system. I swapped the resister, and the heat still works in the '95, and I still have nothing in the '94. Then I swapped the control unit in the dash. The '94 unit in the '95 caused the fan to run constantly when the key was on, regardless of the position of any of the *****/switches. The '95 unit in the '94 made no difference...nothing worked, still.

Obviously the control unit in '94 is bad, but when I switched in what is a known good one, I still have nothing. And after all this, my fuses are still good.

I tried to check codes, and the light on the port under the hood is on all the time. Tough to get a code when you need to push the button until the light comes on, if the light is always on.

So two questions I guess.

What am I missing in the heating system? The fan, the resister, and the control unit, and that's all there is, right? Did I overlook a component?

And, why would the light on my diagnostic port always be on?

Any help appreciated. It's getting cold in the northwest.

 

Did you check for codes at the on board system box?

 

I tried. That's where I'm getting the red light on all the time. I've pushed the button any number of times, and for various lengths of time, turned the ignition on and off a bunch, and even disconnected the battery for a while. The light never blinks or goes out. It just stays on.

 

Think it's time to get in there with a DVM and do some troubleshooting; pretty apparent you got some kind of wiring issue... at least that's my best guess w/o more info. Have you got wiring schematics?

 

I don't, but I think your right . I suppose it's time I get some wiring diagrams

 

Here you go:
http://www.volvoclub.org.uk/tech/ser...ngDiagrams.pdf

 

Thanks for the link. The fun part will be trying to follow a wiring diagram on my phone.

Unless I missed it, I haven't seen any mention of a relay. There's gotta be one, doesn't there? The power for the fan doesn't run through those tiny little wires that go to the heater control unit.

Yes...?...no....?

 

I don't think there is a relay in the ECC system. It just uses an electronic resistor for speeds located in the plenums air stream to cool it.

 

The circuit is fed by fuse 11-5 (30A) which schematic shows as hot at all times; will have to look pwr distribution to see if breaker or such upstream.

Anyway you need to study the AC-HeaterSystem-Auto.pdf doc; it should be available at site I referenced in post #5. You can find it here:
Volvo 850 Maintenance And Service Documents
Specifically here:
http://www.volvoclub.org.uk/tech/ser...ystem-Auto.pdf

Referencing that doc, I explained diag of this system to another poster who had similar issue. Rather than write out again, here's the link. Read the whole thread but study posts #7 and 8. Here it is:
https://volvoforums.com/forum/volvo-...hooting-68570/
Note his car was 98 S70 but i was referencing the 95 850 schematic; essentially they're same but S70 wire color may be slightly different.

Ultimately my best guess is you'll find a bad ground or shorted/open wire somewhere. The doc gives explanation of all ECC pins; you'll need to verify each one is hooked up properly. Let us know what you find.

 

I'd also bet money on an open circuit. The trick is finding it. It helps having two cars. I'm chasing the power flow in the '95, then checking the '94 to see if I've got power in the same places.

I've traced it so far to a big yellow wire that should have power but doesn't. It's in a bundle that disappears into the upper part of the dash, behind the right side of the glove box.

I'll track it further tomorrow. Thanks for the help. I appreciate it a bunch

 

Ok, this is going to be a dumb question I'm sure, but...

What's fuse 11-5? I've got a #11, and I've got a #5, but I don't see anything marked 11-5.

Electrical work is so totally not my thing, and the parts of this car I've got torn apart just to chase one stupid wire is gonna have me in therapy

 

Sorry, never know how much to assume as far as your automotive background.

11 refers to the fusebox under the hood/bonnet near dash driver's side (in usa), so it's fuse #5 (which is a 30Amp fuse) in that fusebox. With volvo manuals, every electrical component type has a generic reference (the first number), - and then a specific number. For example connectors are all 24-x; speakers are 16-x, etc.

To troubleshoot something like this, you really need to at least understand the basics of Ohm's Law, how to test for voltage drop, etc. I can find some good generic instructional links if you're interested; kind of difficult to explain in a post with just words..

BTW: what yellow wire were you talking about?

 

I remember just enough from a high school electronics class to decide I can take something apart. Sometimes it goes back together, other times not so much.

The combination of the wiring diagram and having another car parked next to this one is working for now. Basically, this is what I found...

There's a yellow/violet wire at the control panel (A1) that should have power, and doesn't.




The wiring diagram shows that it comes from 11-31. On my '95 I've got power there, on the '94 I don't, so that's the wire I'm following. The diagram shows that it splits, which it does at a connector by the fan. One wire coming in to the plug on the right, two going out on the other side of the plug, both going to where they're supposed to...one to the relay, one to the control panel. I've got no power at the connector, so I kept following



I traced the wire to the fuse box, and that's where I got lost. It doesn't go to where the diagram says it goes, though I suspect I'm simply reading the diagram wrong. It goes to one of the silver fuses (fusible link?) that you don't see when you pull the small cover off to access the fuses. The yellow/violet wire goes in one side, and a blue wire comes out the other side.



So at this point I realize the wire doesn't go to fuse #31, but in the process of poking everything with my circuit tester I discovered that I had power at the yellow/violet wire. I checked the connector at the fan, and had power there. I checked where it comes in to the control panel and I had power there. I plugged everything together, and the fan works now.

I have no idea what I did, or how I did it, which is part of why I hate electrical work. Jiggle one lose connection and suddenly everything works. There's not always the "ah, I see the broken part" moment. Instead there's the "I don't know, but it works" moment. I prefer the first over the second.

So, lucky me. Put it all together, jump in the car, fire it up....and the headlights don't work now.

High beams work when I pull the stalk, but both low beams are out. I checked the fuses, checked the bulbs, and jiggled lots of relays and connections, and then gave up for the night.

Now I suppose I'll be chasing different wires.

 

Pin A1 of ECC controller is fed by yellow/vio wire which is fed by fuse 11-31 according to schematic; do you have pwr (12V) at fuse 11-31?

If no, see if you have pwr at fuses 30 and 32; these should all be hot in acc or run key position. If none of these 3 fuses have pwr, then it could be the Overload Relay X+ #1. This relay feeds all 3 fuses (30, 31, 32). That's in same electrical box as fuses are but you have to take the larger cover off (a few torx screws) to access; same area as fuel pump relay. It may be working now because you bumped the relay, or like you said, had a bad connection somewhere.

You may have got lost a bit in your 3rd pic. Looking at SystemWiringDiagrams.pdf on pg2 of Power Distribution (pg 39 of 58 in doc) you can see that there are multiple yellow/violet wires; two of them go to Overload Relay X+ #1.

Here's a pic of the fuse box with the larger cover off. The 3 Overload Relays are the 3 small ones in front; #1 on the left (from this perspective), then #2, and #3 on right. FYI, Fuel Pump Relay is the one that says 103 on it in this pic. And BTW, big one on the right is Main HeadLamp Relay; bump that a bit and see if your lowbeams start working...

 

I was going on the assumption that there was only one wire with that coloring, which obviously I shouldn't have. I can see having multiple red wires...they're all power. Or multiple black (or brown) wires...they're all ground. What's the point of having different colored wires if you're gonna duplicate the color in multiple circuits, right? Makes chasing a wire more difficult when it disappears into a bundle.

Anyway, it was the relay. I got this far into it...



...and it turns out that blue connector came loose from the plastic frame, which was a bit structurally challenged to begin with. Yanking on old, cracked plastic didn't help. When I put the headlight relay back in, it just pushed that connector down rather than fully engaging it and making a connection.

Got heat, got headlights. Thank you. Your help was invaluable.

 

Did you try jiggling your ignition switch? How about check your headlight switch? They break internally sometimes.

 

Wow, and you said this electrical stuff is not your thing; think it is now!

So it was the overload relay #2?

 

For the lights, it was the main headlight relay...the one, that has 2 plugs going to it. One of the plugs was loose.

For the heater fan, I have no idea what I bumped or giggled that got power going to it.