Electrical burning smell when heater is on

frostyfriday · Post by **frostyfriday** » Thu Dec 08, 2016 7:29 pm

I have a 95 L400 2.8 diesel I think its an exceed or super exceed. (different labels on either side of the van!)
It has the electronic heater controls.

Last time I drive her I suddenly noticed a burning electrical smell...

I am an electrical engineer so the best way I can describe it is the exact smell you get when you fry a regulator or an IC. Never a good thing!

This occurred for a few minutes before I noticed it (my nose is not good).

My heater had recently jammed warm, and I was not able to adjust the temperature. I was meaning to look at it soon.

So when the smell happened I immediately suspected the heater and tuned it off. Smell stopped. Of course it may have just been the fans circulating the smell but I don't think so because a few minutes later the backlighting of the heater controls died and went out. It has not come back on.
I can still use the up/down buttons to speed up the fan or change the temp (which isn't working) but there is nothing on the display.
I suspect a regulator is blown on the display board.

So I have two main questions

1. has anyone had the burning smell and the display go out. Any pointers to diagnosing that lot?

2 The second problem existed quite a while before and that is my temperature was not adjusting . It was stuck at a temperature that I could regulate by opening the window and letting in some cold air (gotta love Canada). At first if I turned it way up, then way down it seemed to unstick and go to what I then set it too, but eventually that stopped. I had it set low and then my son fiddled with it before I could swat his hand and it was set too hot. Because of this I am inclined to think it may be a physical water control valve that is stuck or gummed up.
Is it more likely to be a mechanical valve issue or is it likely to be a sensor (thermistor or something) that is not reading right and messing up the control feedback?

Any pointers appreciated.

I was supposed to go to Portland today in this cold spell and with all the snow and freezing rain in PDX I would have loved to have taken the Deli but not with a burning smell going on! All I need is for it to completely die in Oregon!

Oh, I have looked at the manuals on this site but the heater stuff doesn't really give much electrical insight.
I would love some more electrical detail. I know I could fix it.

Post by **Growlerbearnz** » Sun Dec 11, 2016 1:07 am

When you couldn't change the temperature, you mean the numbers on the display would change, but the actual temperature would not?

Working from experience with other vehicles here (so not specifically for an L400), but it sounds to me like a jammed temperature flap motor, which might eventually burn out the driver if it were continually trying to move.

I'd pull the control panel and look for evidence of overheating, and then figure out which motor controls the heat and see if the linkage is jammed. If you're lucky it's just a few burnt out traces and/or a blown regulator and/or a driver mosfet.

frostyfriday · Post by **frostyfriday** » Sun Dec 11, 2016 7:37 am

Yes, that's correct. II'll go digging about when I get back from the states.

frostyfriday · Post by **frostyfriday** » Fri Dec 30, 2016 9:33 pm

Sorry people, I just posted another post along this theme. I thought my original was in another Delica website not here! Doh!

Anyway. Turns out the burning smell was a transistor in the MB946619 hearter/AC/Display board. It had got hot enough to melt the plastic rivet that holds it to the pcb. I replaced the transistor and that did not get my display back but I have just discovered a 1ohm series resistor is blown. I will replace that tomorrow and see if my display comes back.

Everything else is working. I just can't see it work! The heat adjustment is still a problem.

Does anyone know where the servo is that controls the flow of hot water to the heater system? I think it is likely jammed.
It would be a great time to hunt it down seeing as I have half the dash apart.

frostyfriday · Post by **frostyfriday** » Sat Dec 31, 2016 6:34 pm

So the display is fixed. Replaced the 2SA1307 PNP transistor (I don't think it was blown) with a TIP32C (It was all the local hobby shop had).
I also added a heatsink to the transistor.

There is a 1 ohm or 100ohm resistor (couldn't read it because it was burnt) in series with the emitter (pin3) It had blown. I replaced it with 1ohm 1/2W.

I am hoping the overheating was not a result of some other problem. I will report back if it turns out it is.

I am still looking for the servo that controls the heat. Any pointers to where it is located would be greatly appreciated before I take half the car apart!
Tomorrow I will start to take apart the lower part of the dash to see what I can see.

frostyfriday · Post by **frostyfriday** » Mon Jan 02, 2017 11:56 pm

Found the servo.
It is in the center of the dash at the very bottom of everything. A little rectangular black box with a small metal frame attached to it and a control arm that adjusts the mix of cold/hot air. I had to remove all the lower trim starting at the drivers side to get to it.
When I removed it, manually operating the control arm changed the heat so I figured the servo had to be bad.
I took it apart (remember the arms position), took the motor apart, took some armature measurements which didn't look right so I figured cleaning may help. It did. I got around 15-20 ohms per motor winding after cleaning whereas I was getting 1 ohm on one before cleaning. I think the dust from the brushes was causing a problem.

I put it all back together and presto I have heat! Adjustable heat. Just as well cause I was fixing it outside and it was below zero. I was starting to get cold...

Friso Stolk · Post by **Friso Stolk** » Mon Jan 09, 2017 6:34 am

Hi there
My front heater blower motor won't turn on but the display works.any ideas on where the fuse is or how to test the motor? L400?
It sounds like you've been there done that.
thanks

frostyfriday · Post by **frostyfriday** » Mon Jan 09, 2017 1:29 pm

I didn't have any issues with the blower so I am not sure. Not even sure exactly where it is. I could hear it blowing in the front though. I wasn't paying attention to it. Someone else will know. Also look at the manuals that are listed on this site. That may show you where it is. Certainly check those fuses first though because it is not a trivial job accessing the heater stuff.

There are fuses under the steering wheel. Maybe there. Also in the engine compartment but I do not think any of them control the blower.

Once you get access to the motor, just take it out and connect it to 12V. Of course you need some basic electrical skills or you may cause more harm than good...

Simon84 · Post by **Simon84** » Mon May 08, 2017 9:22 am

I too have noticed an electrical burning or burning plastic type smell from time to time. It does not seem to be related to the heater operation though.
I have not opened things up to investigate as it is intermittent and seems to have stopped happening.

What I have noticed is that since this happened on our road trip to the west coast last Christmas (on the Coquihalla) it seems to me that the fluid inside the artificial horizon/tiltometer thingy has gone down. So I suspect that in the cold temps that something cracked and the fluid leaked down in to the heater core or something else.

Does this sound realistic?
Has anyone else had this happen?

Also, my heat temp servo is done for and heat is controlled by a piece of wire hanging down under the glove box to go from hot to cold.
I will try to take it apart and clean it.

frostyfriday · Post by **frostyfriday** » Mon May 08, 2017 3:25 pm

Mine was cracked too, but I do not think that had anything to do with it. It is very unlikely that fluid got into the controller.

The control of that servo happens all the time, not just when you need heat so it could be the problem. Mine did not blow right away either. It took a few months.