Re: heater aggravation


"DubiousDude" <dubiousdude@xxxxxxxxx> wrote in message news:b8944bdd-3f52-472f-8fd6-bd11c8a98627@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Apr 12, 4:01 am, DubiousDude <dubiousd...@xxxxxxxxx> wrote:
I've posted a few threads in the past few years about the heater in
my 97 Tercel (no AC), and how it causes respiratory aggravation long
after a drive. Absolutely no signs of core/coolant problems, fan
changed twice, and heater resistor cleaned. I was going to change
the resistor, but the wrong replacement resistor came in to my
mechanic. The 2nd attempt will occur in approx 2 weeks.

However, I found that removing the toyota rugs alleviated the rubber
smell. I can understand why, since the air down at the feet is much
warmer than heated air coming for the face/windows. It only helps a
bit, since the aggravation persists, and I am beginning to suspect
super dryness as one main contributor. How does one deal with the
problem? In a home, I'd just humidify the air.

Another possible cause is the design of the resistor. The mechanic
showed me the resistor, which looks like metallic coils, anchored
into a ceramic-looking block. If the coil is indeed metal, I don't
that that would release anything into the air when heated. However,
the anchoring block might. If it is ceramic, less so than if it was
plastic. I've surfed the web, it was described as plastic -- does
anyone know if this is true?

If if the resistor's anchoring block was ceramic, there is less
chance that it's the culprit. Ceramic doesn't strike me as
out-gassing under heat. However, I need to keep in mind that even
when I had ceramic home heaters, it smelled funny and aggravating.
The housing of home heaters are often plastic,

ransley <Mark_Rans...@xxxxxxxxx> wrote:
Probably mold in system, its common.

"DubiousDude" <dubiousd...@xxxxxxxxx> wrote: On Apr 12, 8:11 am,
That's one of the early candidate causes. I brought it around to
half a dozen places years ago, and the assessment was that it is
certainly not. I had an antifungal mist treatment applied to the
ventilation system to no effect (Ziebart). I had internal detailing
done just in case (Ziebart) and very early on, I had the engine
shampoo'd even though it was unlikely to be the case. I also
avoided Krown this year so as not to obfuscate any sleuthing that I
may conceive of.

I'm currently trying to focus on understanding the resistor better.
What the coil material and the anchoring block material is, and
whether it is plausibly introducing something into the air when
heated.

Also, it was established in an earlier thread that the 97 Tercel is
somewhat exceptional in that there is no sensor control of coolant
to the heater. The amount of heating is controlled by changing the
fraction of air that is blown by the core (perhaps according to the
associated manual dial on the dashboard?). What exactly does the
heater resistor do in this case? In electronics in general, there
are thermistors that provide negative feedback to prevent
overheating. I think that mention was made of the heater resistor
controlling the fan, but I've never noticed the fan speed changing
except in response to the dashboard control.

On Apr 12, 2:08 pm, "Jeff Strickland" <cr...@xxxxxxxxxxx> wrote:
The heater resistor is merely a speed control for the heater motor.
The motor runs at LOW, MED, or HIGH, the resistor is the device that
shunts some portion of the circuit to ground so that the motor gets
a different voltage for the different speeds. The resistor does the
most work in LO, and the least work in HI, bu tthe work it does has
no bearing on the amount of heat in the car, only the speed at which
the air is blown out of the respective ducts.


Hi, Jeff,

Thanks for the detailed explanation. It confirms my understanding of
how the ventilation works. I'm focusing on trying to characterize the
problem with the system in ventilation mode rather than circulation.
My original post was written about that scenario.

When you say motor runs on LOW, MED, and HIGH, I'm not sure whether
you're talking about the dashboard control...My dash has four (not
three) fan settings in addition to "off". Assuming that you mean the
dashboard control, this is a very different understanding of the
resistor than I had. Basically, it means the heater resistor is being
used as a stepped/tapped variable resistor to control the fan.


Whatever. There could be 50 speeds, the theory is the same, just the implementation of the resistor changes.

The normal fan speed selection was orignially set to three speeds, some automakers still use three, some use four, and the hign end cars have variable speed motors.



As I mentioned in my original post, I thought the role of the heater
resistor was temperature-dependent resistance that controlled the fan
so as never to let the heater core get too hot (hence it's location on
the heater?). That is, when temperature increases, the circuitry is
such that the fan speed increases in order to mitigate the heating up
of the core. However, I also found this assumed role for the resistor
to be confusing, since I've never noticed the fan speed changing
except in response to direct control from the dashboard lever.


No, that's not the case. The fan runs at one speed, the one you set it to. They like to put the resistor in the cold air stream to help it stay cool -- the byproduct of the job it does is heat, the cold air stream helps control that heat. The heat has no value in terms of passenger comfort -- it not part of the heating system. It's more like the byproduct of a light bulb is heat. You get the heat, but the heat is not very desirable most of the time.



Could you please confirm role of the heater resistor with regard to
the two functions in the preceding two paragraphs? My background is
in electronics, so I realize that there are numerous ways to set up
circuitry for either of the two roles. I'm not so much interested in
the electrical details as I am about the central role of the resistor,
out of the two possibilities above (unless both are incorrect).


I described the role as a shunt to ground. In general, this is probably reasonably accurate. As a practical matter, we're probably not really shunting voltage to ground, we shunting the current.

Let's say there are 30A available in the circuit -- it doesn't matter the actual amps, but the real number is lower and the fuse will tell you what it really is. So, the fan on HI takes all 30A, and it spins around at a furious rate -- the resistor is out of the circuit at this speed. When the fan is needed at LO speed, they put a honking big resistor in line that only lets 5A get past -- again, a number that I pulled from my ass to illustrate the idea. The motor on 5A spins very slowly, and you get LO speed operation as a result. The resistor gets hot, so they put it in the cold air stream to help keep it cool. They tap into the resistor for each additional speed they give you at the control panel. If you have 4 speeds, there are three taps on the resistor that each pass more current than the tap before. The first tap has the highest resistance and caps the greatest amount of current, leaving the least amount of currennt to drive the motor. The next has less resistance, passing more current to the motor so it runs faster, the next is faster still. Finally the resistor is bypassed and the fgan runs at full speed.




On Apr 12, 12:05 pm, "Jeff Strickland" <cr...@xxxxxxxxxxx> also wrote:
The resistor you are talking about is not a heater. It shunts
voltage to ground, changing the voltage at the fan motor to affect a
change in the speed of the motor.

I'm not understanding what the aggravation is.

It produces a dry cough that persist for long after a drive (I get
weird looks during workouts because it sounds like I'm dying, and
indeed that's what it feels like).

The duct work collects air from the base of the windshield and
routes it into the cabin. There is a radiator and a fan built into
this duct, the fan changes the speed of the air passing through the
duct, the radiator heats the air. There is nothing that should cause
any respiratory issues that would not exist if you were simply
walking down the roadway that you drive upon.

Having said that, IF your car has any sort of mold or mildew inside
(in the passenger compartment) AND you keep the ventilation system
on the Recirculate mode, then that mold and mildew is being picked
up and spit out over and over again through the duct work. In
recirculate, the duct picks up air from the passenger side footwell
INSIDE OF THE CAR and spits it out from the duct as you select --
windshield, dash vents, floow vents, or a combinatioin of these.

Over the years, I've attributed it to various things, which I've
whittled away at. For example, at one time, there was a serious oil
leak, and you could smell it everywhere outside the car. I thought it
was related to the respiratory aggravation, but that leak was fixed
long ago. I also decided to forgo Krown this year in the remote
chance that it is related. I chucked the matts away after Ziebart
detailing, and that got rid of the hot rubber smell. I now step right
onto the fur above the bare metal that is the floor of the car (not
great for the floor, but then the car is not going to be tolerated
much longer unless I manage to solve the problem).

Over the years, I've also brought it to many places (dealer, chain
garage, two of the best mechanics in the city, detailing/cleaning
places, asked all friends/passengers) and subjected it to all manner
of cleaning/treatment. Mold has been ruled out.

Given all that, I also thought that there is nothing that should cause
any respiratory issues that would not exist if you were simply walking
down the roadway that you drive upon. However, there is plastic all
over the front of the car, and I wonder if they might be outgassing
when heated. In particular, I noted that the hot air coming out at
foot level is much warmer than that coming out to the head or the
windshield. I mentioned that this would explain the hot rubber smell
prior to removal of the matts. As well, the heater resistor is
anchored into a plastic/ceramic block. I was wondering if that
plastic might outgas when heated. The ceramic I would suspect less
so, though comments are welcome on the plausibility of that too.

Well, you certainly sound as if you are having problems that you have isolated to the car. I assume that you ride around in other cars that do not give you problems with your breathing.

I can't escape the feeling that the problem you have is one that might come from the relative low quality of the Tercel in the first place. I wonder if you have trouble in other Tercels, or in upscale models such as the Camry or Avalon. I'm not suggesting that you buy a new car, or stop being so damn cheap <wink>, but as a matter of further isolation, there might be some research value to getting away from your Tercel to see if your breathing issues clear up.

If you are so sensitive to outgassing from plastic, then I would guess that your car riding experience has to be very uncomfortable from almost any car that you get into.

Please don't read my comments as if I'm dissing on your relative wussiness -- I'm not very tactful sometimes and I simply don't have the words to describe what I read into your health issues that sound better than the ones I'm using.

In any case, I'm having a very difficult time coming up with a solution that points to your car as the source of your troubles. It sounds as if you've spent quite a bit of money chasing this down.




.

Relevant Pages

  • Re: heater aggravation
    ... Absolutely no signs of core/coolant problems, fan ... changed twice, and heater resistor cleaned. ... resistor, but the wrong replacement resistor came in to my mechanic. ... since the air down at the feet is much ...
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  • Re: heater aggravation
    ... controlled the fan so as never to let the heater core get too hot ... found this assumed role for the resistor to be confusing, ... have isolated to the car. ...
    (alt.autos.toyota)
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    ... controlled the fan so as never to let the heater core get too hot ... found this assumed role for the resistor to be confusing, ... have isolated to the car. ...
    (alt.autos.toyota)
  • Re: heater aggravation
    ... Absolutely no signs of core/coolant problems, fan ... changed twice, and heater resistor cleaned. ... There could be 50 speeds, the theory is the same, just the ...
    (alt.autos.toyota)
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