Re: heater aggravation


"DubiousDude" <dubiousdude@xxxxxxxxx> wrote in message
news:e36ecac3-6504-4017-8ffe-5121f15ee8ba@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Apr 12, 5:05 pm, "Jeff Strickland" <cr...@xxxxxxxxxxx> wrote:
"DubiousDude" <dubiousd...@xxxxxxxxx> wrote:
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.

That's interesting. Sounds like it would be more aptly referred to as
a varistor for controlling the blower fan speed rather than heater
resistor.


The resistor pack is for the fan motor, not the heater.

Based on the descriptions at these sites:
http://www.wisegeek.com/what-is-a-varistor.htm
and http://en.wikipedia.org/wiki/Varistor the resistor pack for the fan
motor is not a varistor.

When the fan is set at its highest setting, the current goes directly to the
fan motor without passing through the resistors so the resistors do not heat
up because they are not in the circuit. If the respiratory aggravation is
worse when the fan is set to high speed, the resistors are unlikely to be
the cause of the aggravation.

When the fan speed is set to the second-from-the-highest position, current
passes though one resistor to create an additional load to slow down the
fan.

When the fan is set to the third-from-the highest position, current passes
through another reisitor which higher resistance than the furst resistor to
slow down the fan further.

When the fan is set to the fourth-from the highest, or lowest position,
cureent passes through both resistors in series.

You mentioned before that you thought that the heating system regulated
cabin temperature by varying the amount of outside air passing across the
heater core. This is not correct. When you adjust the temperature control
for the heater, you are moving two rods that are connected to the heater
valve on the firewall. When the control is moved to the hot position, the
valve is opened, allowing hot coolant to circulate through the heater core.
When the control is moved to the cold position, circulation to the heater
core is closed off.




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.

From your description, it sounds like the resistor is in an
approximately series configuration with the fan rather than being in
parallel.


Yes, the resistors are in series with the fan motor.

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.

Generally no, but in two other cars belonging to friends/colleagues, I
detect some kind of smell that could becoming aggravating over time.
I did not got exposed to them for nearly long enough to know. It was
an older model Saturn, and a medium age Hyundai who's make I don't
recall.

There is a very plausible possibility that they don't invoke prolonged
coughing afterward because I've hardly ever been exposed to those two
other cars. Hence, my breathing passages haven't been abused by them
in a sufficiently consistent basis so as to be up in arms and ready to
inflame at the slightest exposure.

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.

Hey! It's cheap, I know, I know. Situation was very different when I
got the car. Now I have more flexibility in choosing a vehicle, but I
need to know what are the sticking points (such as the cause of the
respiratory problem) so that the next purchase actually addresses the
problem rather than simply fulfilling a list of nice-to-have features.

I agree with the merit of research. Getting away from the vehicle on
a consistent enough basis to be sure that the problem is isolated to
my car/model alone...that would give the confidence in choosing
another car.

Getting away from the vehicle on a consistent enough basis would also
be hard to achieve because it means experimentally renting cars for
extended periods. Apart from weekends, I drive infrequently, so a
rigorous test would entail prolonged rental to guarantee enough
repeated exposure for a confident assessment.

As an alternative, I could rent just during the weekends, but I
wouldn't be guaranteed of getting the same car. Being exposed to the
same car over a long period is important to such a test. Still, being
exposed to many cars without developing a respiratory problem would
still be telling, though less informative.

Regardless of how I rent, it would be expensive, I would need a second
parking space, and it would be a PITA to do a separate rental each
weekend. I'd be tempted to cheat and just use a taxi or transit when
I need transportation during the weekend.

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.

I understand the logic, and want to emphasize that I don't know that
the plastic is the problem. Apart from heating, it's just one of the
few things that distinguish the air outside from the air inside, hence
a possible cause of the problem.

I am bothered by the heated air in the two other cars I mentioned
above. Not to the same degree, but as I describe above, this might be
due to lack of consistent, repeated exposure.

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.

Wussiness is probably from consistent exposure to the same aggravant,
be it dry air or something else. Respiratory tissue tends to become
sensitized to the condition and over-reacts with further exposure.

I appreciate your explanation of the heater resistor, and attempt to
understand my long-standing problem.

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.

Time and money, out of necessity. My characterization of the problem
as resulting from the car is because, empirically, there is a strong
correlation between the periods of coughing and having driven the car.
The longer the drive, the stronger the correlation. The periods of
coughing usually follow use of the car.

The only thing I can do is to continue to seeking a solution, whether
it is further things I can investigate or try with my current car, or
it may be the case that I have to just try another car without knowing
the cause of the problem with any confidence. Another possibility is
to go car-less (or at least, devoid of car ownership). In this city,
it would be a huge set-back, especially with my current residential
location.

By the way, you dispelled my misunderstanding that the heater resistor
(better named varistor for blower fan speed) as a thermistor to
stabilize the blower fan speed through negative feedback. Part of the
reason that I had this misunderstanding is that I thought it was
intimately in contact with the heater. Would it be accurate to say
that this is not the case i.e. the heater resistor is not actually in
intimate contact with the heater, or conduits that deliver coolant to
the heater?


See my explantion above regarding how the blower resistor pack works.

The resistor pack does not contact the heater core or hoses connected to the
heater core. The pack protrudes into the airflow delivered by the blower
fan.

In addition to the question of the resistor being in contact with the
heater, would you know what material the resistor is made of? That
is, are the coils metallic, and is the material they're anchored into
made of plastic or ceramic? As I mentioned in an earlier post, I
suspect ceramic less than plastic, though even ceramic space heaters
for the home have a characteristic odour.

The resistors are simple metal coils that are mounted on metal legs that are
anchored in plastic. The metal legs dissipate the heat generated by the
resistors so that the plastic does not melt.

Before you change the resistor pack, try driving with the fan on high speed
or off so that the resistor pack is not in the circuit and not generating
any heat. If the condition persists, the resistor pack is not likely to be
the cause.

There are a few other things that I recommend you try:
1) shampoo the interior in case some allergen has accumulated in the carpet
and upholstery.
2) check to make sure that all underbody heat shields are in place,
especially if there is an aftermarket exhaust system installed. You
mentioned that the floor heaters produce hotter heat than the dashboard
vents, and this may be due to a missing heat shield.
3) check to make sure that there are no exhaust leaks
4) check to make sure that there are no exhaust obstructions.
5) ask your doctor if it is possible to identify the source of the irritants
like through an allergy test. For example, you can ask to see if automotive
or diesel exhaust fumes being drawn into the car's ventilation system are
causing the aggravation.

If you decide to go the rent-a-car route, keep in mind that some newer
vehicles have a cabin air filtration system that may trap any airborne
particulates that are causing the aggravation, so try one of those vehicles.

--

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
    ... 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
    ... 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
    ... 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)
  • 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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