Interior Defrost not working well

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Interior Defrost not working well Empty Interior Defrost not working well

Post by 76 Malibu on Mon Aug 25, 2014 3:11 pm

Recently while driving the car on a hot humid rainy day, I found the car's defrost system was not working well. The car's interior was fogging up even with the defrost on. Anyone have any idea why it's not working well? I was thinking maybe a pin-hole leak in the heater core, but I don't have any sweet smell in the car.

My Malibu is a factory non-A/C car and for whatever reason the vent system has never worked well. When the windows on the car are up, the air flow from the vents virtually drops off to nothing, so you always have to keep the windows cracked which is irritating. I have owned other non-a/c cars from this era and this one has by far the worst vent system for airflow with the windows up. I don't know if it was a design flaw or there is something wrong with my car.
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Post by dynchel on Mon Aug 25, 2014 4:15 pm

I think they suck by design.  Mine also is a non a/c car and I couldn't have described what mine does any better than you did.  I only drive my mine on windows down nice days so its tolerable.
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Post by Joe73 on Mon Aug 25, 2014 5:19 pm

I have a non-a/c car as well. Yes, they are horrible with the windows up especially when its raining. Not much you can do about it.

When a/c cars are in high humidity (like its raining) the defrost position cycles or even turns on your a/c compressor. Even in the winter. The a/c system removes moisture from the interior. Hence the puddle of water under a car with the a/c on.
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Post by thatfnthing on Mon Aug 25, 2014 5:41 pm

Joe73 wrote:When a/c cars are in high humidity (like its raining) the defrost position cycles or even turns on your a/c compressor.  Even in the winter.  The a/c system removes moisture from the interior.  Hence the puddle of water under a car with the a/c on.  

Not just in high humidity, since the car does not measure that. An A/C car engages the compressor every time you are directing air to the windshield -- even if it's one of the late model cars where you can have part defrost, part floor. The point is that without drying the air, you're not going to get far clearing the window. On a non-A/C car, your only option is to crank the heat, the idea being that if the window is hot, the moisture will not condense on it.
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Post by 76 Malibu on Tue Aug 26, 2014 8:44 am

Well that's disappointing if this is as good as it gets. I wish there was some modification we could make to these cars to improve the interior air flow when the windows are up. It's almost as if the door jamb vents don't function properly.
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Post by thatfnthing on Tue Aug 26, 2014 8:58 am

Those are there primarily to equalize pressure so that when you slam the doors shut with the windows up you don't blow your eardrums out.
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Post by 76 Malibu on Tue Aug 26, 2014 1:31 pm

I thought they were there to exhaust the interior air, like this diagram:

Interior Defrost not working well Fig1A03
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Post by thatfnthing on Tue Aug 26, 2014 2:34 pm

I'd read it somewhere -- maybe it was inaccurate or incomplete. IIRC, though, the vents have flaps on them that only allow air travel one way (into the quarter), so I don't see how they could be effective at equalizing in the other direction. Dammit, now I'm gonna have to go home and unbolt one...
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Post by driveit on Tue Aug 26, 2014 8:05 pm

thatfnthing wrote:I'd read it somewhere -- maybe it was inaccurate or incomplete.  IIRC, though, the vents have flaps on them that only allow air travel one way (into the quarter), so I don't see how they could be effective at equalizing in the other direction.  Dammit, now I'm gonna have to go home and unbolt one...

That was funny. Let us know how that turns out!
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