Re: heater aggravation


"Jeff Strickland" <crwlr@xxxxxxxxxxx> wrote in message
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"DubiousDude" <dubiousdude@xxxxxxxxx> wrote in message
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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.

This is incorrect. The role of the resistor is to reduce the current going
to the blower motor to slow down the fan.


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.


A resistor does not shunt voltage or current to ground. The description in
the paragraph above is totally inaccurate. See Tegger's description for a
correct explanation of a resistor's function.
--

Ray O
(correct punctuation to reply)


.

Relevant Pages

  • Re: heater aggravation
    ... Absolutely no signs of core/coolant problems, fan ... changed twice, and heater resistor cleaned. ... since the air down at the feet is much ...
    (alt.autos.toyota)
  • Re: heater aggravation
    ... resistor, but the wrong replacement resistor came in to my mechanic. ... since the air down at the feet is much ... The resistor you are talking about is not a heater. ... changing the voltage at the fan motor to affect a change in the speed of the motor. ...
    (alt.autos.toyota)
  • 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)
  • Re: Simple fan control
    ... cheap ceiling fan here in SE Asia; ... lower speeds. ... I decided that the inductors, in effect, ... they don't have the power or rather heat dissipation like a resistor ...
    (sci.electronics.design)
  • 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 implementation of the resistor changes. ...
    (alt.autos.toyota)
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