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How to: Prevent Fire (clean blower resistors)

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Ok so the last couple of weeks I've been getting this odor that seems to come out of the heater. It smells like burning wood. Now before you call me all sorts of names I'm pretty sure sure it is not coming from someones backyard or chimney. It always smells the same, goes away if I shut off the heat and seems to come on randomly. I know this is kind of a stupid topic but I cannot find anything under the hood that could be causing this and I was wondering If anyone else has experienced this. I bought a fire extinguisher last weekend just in case it is something to worry about.

thanks

ticker

Edited by Pezzy

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Oddly enough, I had a similar issue....I looked underneath my truck, and there was a piece of wood lodged between the cat and the body. I'm lucky I caught it and it didn't burn my truck down. :blink: :eek:

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Ya know what? I checked the engine bay butI didn't look down below-

thanks vengeful

I'll check it out

ticker :aok:

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If that doesn't pan out to anything, its possible that your in cabin air filter (if equipped) needs to be changed - or something got into your heater fan...

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Hmmm.... that's exactly what the previous owner said before the smoke began...

 

Does the smell start when the cabin fan is on speeds 2 or 3, and then dissipates when you turn the fan to settings 1, full, or off?

 

If so: STOP using the ventilation fan on any settings except off or maximum until you check this out - when the fire starts (and the smell is telling you it is just about to...), it is hard to put out - until it melts/burns through the plenum and makes a hellacious mess of things....

 

Seriously, this can be a real mess. The fire will start inside the plenum and blow massive amounts of smoke into the cabin, blinding you.

 

What's happening?

 

There is a resistor pack for the blower motor. This is what allows you to have multiple speeds. It works by adding resistors in line with the motor. Since the motor draws so much current, a bunch of current goes through the resistors. Which means a whole lot of heat. The resistors would glow red hot and ignite things without a lot of air blowing across them. When fan is off, no heating. On setting 1, three resistors get a little hot. On 2, two resistors get hot. On setting 3, one resistor gets REALLY hot. On full/maximimum, the pack is bypassed and does not get hot.

 

Where are these resistors? In an ideal location where lots of air will blow across them when they need cooling. Inside the heater plenum, after the fan and before the air conditioner evaporator and heater core. Works great with one possible problem - If you park under trees on a regular basis and don't clean out the fresh air intake regularly (the grilled area between the hood and windshield), small pieces of leaves and pine needles can work their way down through the fan and get into the plenum. Over years, they build up. Once you get about 4" of build up in the plenum, they start touching those resistors. Run the fan on speed 2 or 3, and those resistors will get hot enough to dry out and eventually IGNITE the debris.

 

By the way, this is not unique to Pathfinders. Pretty much all vehicles I know of are subject to this.

 

How to fix? Easy.

This is how you would do it on an left hand drive '87 - others are likely similar:

1) Remove the glove box.

2) Remove the metal plate you see. You are now looking at the ventilation system plenum. It is fiber reinforced plastic. The fan is to your right, the AC core and heater core are to the left.

3) See that giz bob sticking out into the plenum with a connector plugged sticking out of it? With 4 or 5 fat wires sticking out of it? That's the resistor pack. Remove the two screws securing it to the plenum and pull it out. Look in the hole.

 

4) WHOLLY CRAP! See how much debris is built up? And notice some of it is scorched? Thank goodness you cleaned it out now!

scoop it out with your hand or use a vacuum.

 

Reassemble. Thank your good fortune you did this before the fire. :bow:

Edited by mws
  • Like 3

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Well I was going to suggest that you check the resistor and around it... but MWS did such a great job in his post there is nothing left for me to say, except that "I agree completely!" :aok:

 

Stop using your fan (with or without heat) and check that out!

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WHOLLY CRAP is right. It sounds like even with a fire extinguisher that would be a tough spot to get to. Not that I want to ever have to use it. Looks like I know what I'm doing this weekend. Thanks for such a great description of how to go about remedying the situation. It happened again this morning. I was starting to think I was going nuts because I couldn't find any visible leaf or wood debris in the engine bay or underneath. I'll keep you posted as to how it goes. Hopefully it will stay warm for a couple days, went from below freezing and snow yesterday to sunny and 50's today. I doubt I'll have a chance to look at it until Sunday.

Thanks to all.

ticker ;)

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I couldn't wait till the weekend to check it out-OMFG there was a good three inches of leaves down there. thankyouthankyouthankyouthankyouthankyouthankyou mws! How sketchy is this-total fire hazard. I would highly recommend everyone do this especially on the the older rigs out out there. I don't necessarily park under trees a whole lot but the PO might have.

It was super easy to do, although the screws that hold the metal plate on were torqued really well. Once its open i just put the vacuum in there and sucked it out. DO NOT TURN ON THE FAN UNLESS YOU HAVE ALREADY CLEANED IT OUT-otherwise you will end up with leaves everywhere. I waited and I still got a small flurry because of hold outs.

Sorry no pics because I did it in the parking lot at lunch today. Just follow the directions above, they were spot-on. Once again you all have saved my a$%.

big props to mws for the step by step

have a good weekend yall

ticker -bounce- :bow: :o :cool2:

 

PS-after I did all this I drove home and still noticed the smell-I took everything apart and realized I forgot to vaccum the little box that the resistors are housed in-I think there were some leaf particles stuck in there so just FYI don't forget this step. Now everything is great-no smell no fear and most importantly no fire!

thanks again

Edited by ticker

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I always like to hear stories of fire prevention, good job mws :aok:

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Hey Admins....can this how to be stickied in the Garage section or How To???/

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Hey Admins....can this how to be stickied in the Garage section or How To???/

Yes, please do. *checking this out jumps right onto the to-do list*

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Yes, please do. *checking this out jumps right onto the to-do list*

Yeah you probably should.. as should everyone else. When I first bought my Pathy the fan only worked on high (bad resistor) and when I pulled it to install the replacement there was a lot of junk in there. Although not as bad as what Ticker had, it was still too much.

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SMOKEY APPROVED!!

 

Good to hear that worked out for you!

 

mws, great help!!

 

I'll sticky this thread! B)

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Wellp...I might as well do this, too, as I'm going to be in there anyways tomorrow redoing all my switches...

 

Oh, headliners SUCK! I should just freaking herculine my roof and call it good. :furious:

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Glad I was able to help before you ended up with a "modified" plenum like I have!

 

And remember - this type of problem is NOT unique to Pathfinders - although it appears the pathy may ingest more than average. Most vehicles have the same types of problems to varying degrees. I've never opened a plenum that didn't have some debris in it.

 

Just out of curiosity, I'd like to request everbody add a post to this thread detailing how much debris there was and how frequently they park under trees.

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Rarely park under trees.....found about 2.5-3" of debris, comprised of leaves, paper, dust, pine needles in my plenum, and a bunch of leaves wrapped around the fan part of the blower motor......

 

Not pretty.

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good writeup/maintainance idea. i did mine for the hell of it and took out a bit of debris. nothing serous, but i notice that my blower motor dosent make near as much noise as it used to :shrug:

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dang. i just found this thread earlier today and cleaned mine out by hand and with the use of a vaccum cleaner. i couldn't believe the leafs and other random crap i found in there! all cleaned up now :D

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GREAT.....more work for me...now I just have to check mine out due to curiosty.

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Guest sprint25

:cool2: thanks for the heads up, mine was packed half full of trash along with blower motor housing packed full. i now have heat. thanks

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Pulled the covers off the air plenums off both of my Chevy vans. Guess what? They were both PACKED full with debris.... Fortunately, the resistor pack is located elsewhere in the ducting so less fire risk.

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Once again thanks to the wonderful insight and contributions from the members on this board I have prevented a fire in my blower. Pictures are worth a 1000 words. Again if you haven't looked at doing this DO IT! It's a 10 minute project. Toughest thing is getting the glove box out. The bottom pivot hinge pins are slides (at least on my '91 SE). Rotate them 90 degrees and pull them to the inside. From there it's 8 phillips-head screws and your trusty dusty negative air extraction machine. Check your resistor pack for cack as well. Once cleaned, reassembled and operating you are liable to get a brief odor of, in my case, burnt leaves as I'm sure I disturbed some of the dust in the resistor pack while I was getting the chunks out. This little procedure has to help heat transfer to the heater core and A/C condenser let alone let all the condensate find a much less restricted path to the drain thereby eliminating the "wet floor board issue"

 

Thanks mws! :beer:

 

 

 

th_P1010042.jpg

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Good thing you checked!

 

I planned on "bumping" this the other night because of the number of new members we have... but it slipped my mind. Thanks :aok:

  • Like 1

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Unbelievable!!! I just got done doing this and I'm amazed I was able to go this long without a fire. Thanks. I remember about 4 years back turning on the a/c and smoke coming out of the vents, now I know why. I found a variety of crap in there, from feathers to pine needles and leaves. I wonder how many automobile fires have been started due to this. Thanks again!!

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something else to think about on the earlier pathys and hardbodies,

the resistor wires were held together with a plastic bolt and nut. Sometimes the heat would melt them and you would only have hi speed on the blower.

We went through quite a few of them at the dealership I worked at and we finally just started just replacing the bolt and nut saved the customers a little $.

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