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Old 11-09-2009, 10:25 PM   #1
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Thumbs up TIP: Smell When Run Heat on FULL...

'94 LX currently ~238k

This problem first appeared about two years ago when it was really frigid out.

For awhile, thought I was breathing the exhaust fumes of those cars in front of me. But after about a week or two eventually caught on to the pattern that the strength of the smell was tied to running the blower on full.

QUESTION: What was the smell ?
ANSWER: Burning plastic.

QUESTION: What was the source of the smell ?
ANSWER: The small and large plastic wire harnesses for the blower motor.

SUPPOSITION: The motor was pulling enough amperage to burn-up the plastic wire harnesses so it must be bad right ?
ANSWER: Nope.



QUESTION: So what caused the plastic on the wire harness to burn up ?
CAUSE: The contacts on the wire harness and those on the resistor assembly were severely corroded. (rusted in fact)




The motor is in fact, good. The bearings are good and turns easily, even when heated. Replacing the motor only provided temporary relief.


RESOLUTION: To resolve the problem, the metal contacts need to be replaced. Cleaning them up will be just as temporary. Ordinarily they should not corrode in that manner. The alloy used in manufacturing them is defective.
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Old 11-09-2009, 10:39 PM   #2
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Re: TIP: Smell When Run Heat on FULL...

Are you sure it's the plastic of the blower that burns? Try to turn on the front defroster, cause it's another blower. If the smell still, something else is burning under the hood. Check also on main radiator if it's clean. It happens also when engine is full cold?
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Old 11-09-2009, 11:32 PM   #3
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Re: TIP: Smell When Run Heat on FULL...

Hi Serge.

Actually there is but one blower motor for the 'scorts in the US. As far as I know this is true for most if not just about all passenger/sedan vehicles. Minivans will typically have two blower motors; one for the back. Different sets of "doors," sometimes servo-controlled are all that are used to redirect airflow for the front defroster in sedans and vans.

High resistance or poor conductivity is what causes this problem. If you had a very low "volume" of sand slowly trickling through a very large pipe, that pipe wouldn't necessarily get very hot would it ? Well, what if you had a very high "volume" of sand rapidly flowing through a very small diameter pipe ? The friction increased by the pressures would make that pipe very hot wouldn't it ? When the material in those contacts corroded, that effectively reduced the diameter of the pipe. If the contacts were larger and their surface-to-surface contact area increased, that might've helped to mitigate or at least, further delay the onset of excessive temps.

This principal is why lower gauge wire (meaning thicker) is used for high amperage draw devices such as household vacuum cleaners. Pulling large amounts of power through a small orifice creates a lot of "pressure" or resistance. The material under so much "pressure" begins to heat up; or converts some of that energy into heat. With the contacts being corroded that effectively reduces the contact surface area capable of efficiently conducting current. Sweeper manufacturers will not recommend this in their manuals, but if you've ever tried to run an aged 12 amp vacuum cleaner through a cheap, thin extension cord, after some time you may notice that the cord will get warm and may even damage it's own insulation.

As far as the diagnosis, I wouldn't have labeled this a "TIP" if I weren't sure.

If you see inconsistencies and/or holes in the plastics of the wire harness, and/or you see that the contacts are corroded, then they need to be replaced.

In my case, there are about three holes between the two wire harness plugs. The most corroded contact is the one that has burned the huge gapping hole through it's compartment in the wire harness.
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Old 11-10-2009, 10:41 AM   #4
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Re: TIP: Smell When Run Heat on FULL...

Of course a thin wire heats more than a large wire when it draws more current. Especially if it's corroded. So you need to replace the harness.

I didn't know that you were sure about the smell source.
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Old 11-10-2009, 10:48 AM   #5
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Re: TIP: Smell When Run Heat on FULL...

interesting thanks for the heads up
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Old 11-10-2009, 12:13 PM   #6
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Re: TIP: Smell When Run Heat on FULL...

In my case it is important to notice that the contacts burned a hole on the outside parts of the plastic harness. This is because of the way they were assembled; with the large flat back side of the contacts facing the outside walls of each compartment. Had they been assembled differently, that might've introduced the possibility of shorting. (which would damage the wiring and/or blower motor control switch)

When assembling the replacement harness, (get them from a junk yard,) be sure that the back, flat side of the contacts are all pointed towards the outside walls of the plastic harness, as they were before.
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Old 11-13-2009, 03:03 PM   #7
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Re: TIP: Smell When Run Heat on FULL...

I sometimes smell antifreeze when I run the heat. It isn't the heaer core either. I don't get the smell when I use recycled air, I only get it when I use outside air. Presumably I am only smelling this because of my tiny coolant leak somewhere in the engine (which I supect is near the thermostat housing). How is that for a confusing smell when I run the heat!
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Old 11-14-2009, 04:11 AM   #8
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Re: TIP: Smell When Run Heat on FULL...

I used to get that as well until a crack in the head was repaired and bought an HGasket set. Also left a thin film on the inside of the window. Common failure point is on the corner exhaust side of the fourth cylinder. I was loosing minute amounts of coolant and despite driving a lot of miles, had to add once a month if that. Gradually got worse. Upon disassembly and cleanup, saw one crack running from the exhaust manifold 2nd & 3rd cylinders to their respective exhaust valve. It's the cast iron header and iron block on aluminum head that causes the stress fractures. Common problem for vehicles of this era. Neons and Saturns heads are often irreparably damaged. Post repair no more film, no more coolant smell.
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