In my 2004 Dodge Caravan, if the heat-A/C system selector is set to any
(ventilation output) position other than defrost, I can slide the
temperature selector all the way down (cold) and all I'll get is untreated
outside air unless I deliberately hit the A/C button. However, if the
selector is turned to the defrost (windshield) position, the A/C will
automatically come on if/when the temp selector gets close enough to the
Is there any way to disable this automatic connection between the A/C
compressor clutch and the defrost selector? I'd really like to be able to
get just plain outside air through my defroster vents and I can always hit
the A/C button if/when I want A/C (just like for any other ventilation
position on the selector dial).
The A/C compressor "on" with the defroster button pushed is designed to come
on for safety reasons. It is there to pull moisture out of the car and keep
condensation off the windshield. There is no setting that will by pass this
Glenn, i thinnk that design might be a great idea but it is one of the
useless desings I know. when people need the put the blower to the
defrost mode, usually it is colder outside. People donot want cold air
blow to their face so they put it in hot position which disables the
AC. so AC runs but does not do anygood. Am i right?
The analogy for the pulling moisture is same for the removign
condensation. The people put it on heat/warm settign so they bypass
the evaporator of AC. So it does not make any difference if you run
the AC because no air flows thought the ac part.
May I ask you if you put the blower in hot or cold setting when you
try to remove moisture in a cold day. You either use AC explicitly to
remove moisture on hot days, or you donot care because it does not
block your view.
The only way the evaporator is going to be bypassed is if you
whack at it with a saws-all.
I've had plenty of HVAC cases apart, I have yet to see one where
the intake air doesn't flow thru the evaporator first.
There simply isn't enough space available to have separate air
intakes for the heater core and the AC evaporator.
You don't put the "blower" in hot or cold setting, the blend door
determines how hot or cool the output air is going to be.
The "blower" settings simply determine how many CFM of air will
You totally misunderstand how a HVAC system works on any vehicle
built in the last 30+ years. AC and heat(defrost) can (and do)
Maybe I should take apart my part to see how the air flows through the
Putting blower to hot position is an honest mistake but I expect you/
anybody to figure out what I meant. What I meant is Blending door
button (I'm sure it has a special name for it also, but please try to
understand what I mean).
You are kinda right because today even it is at 65s here, I got
moisture on my windshield due to rain. So I accept you can get
moisture on winshield even on hot weathers.
Summary: If we follow air from out of the car to inside , The air
first passes through AC evaporator, then depending on the positon of
blending valve bottun, The air might pass through heater core or
bypass the heater core. And then the air is sent directly to air
IS it right?
What I thought is, AC evaporator and Heater core are sitting paralel
to each other. Blendign valve sends the air either to evaporator or
heater core or both depending on setting. and then the air is sent to
air ducks. I guess the flow diagram I mention latter is wrong.
Did I get it this time.
On Tue, 13 Mar 2007 10:33:05 -0700, uccoskun wrote:
Wrong again, kiddo. The AC compressor can run regardless of the
temperature setting. That's how it works.
I put my *temp control* on warm, and the *blower* to a speed setting
appropriate for the conditions (usually high when first starting the car
with moisture on the windshield).
Again, the vehicle AC system *will* remove moisture from the air,
regardless of whether you have the temperature setting on "cold" or "hot".
"Ubuntu" -- an African word, meaning "Slackware is too hard for me".
In the old days it was a general piece of wisdom that if your defroster
wasn't de-fogging your windshield well enough or fast enough, you activated
the A/C, even with the temp on high, to help dry things out. However, since
I know that, I would like to be able to *choose* to do that or not. I really
would like to be able to get plain fresh air through my defroster vents, but
apparently the designers have decided that I'm incompetent and have
automated things the way they feel it should be done. Short of rewiring the
car from the ground up, including completely re-programming the brain that
seems to be in control of *everything*, I guess I'll have to live with the
"you're an idiot -- leave everything to us" design...
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