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Discussion Starter #1
I"ve had to almost always have the air distrubution set to defrost and floor to keep the windows from fogging up... About 2 weeks ago, I noticed while idling for an extended period of time, that the A/C compressor was cycling on and off, even though the A/C switch was off and the indicator light wasn't on. To verify this, I switched the air distrubution to the dash vents, and the compressor stopped running. I tried all kinds of combinations and switching back and forth to Defrost while the A/C was already on or already off, and it definitely feels like Defrost *always* uses the A/C.

I've owned 25+ cars, and none of them have done this.

Anyone else notice it? Is this particular to Hyundai?

Since I noticed this, I've been mostly using the floor-only setting, and that has kept the fogging to minimum, and I've seen my avg MPG go up by about 2MPG since...
 

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my 96 explorer did this, whenever i ran the front defrost, the compressor ran, it was normal

my elantra however didnt have a AC so I didnt ever worry about it,

in this car I just slightly crack the front windows and it helps alot, or the sunroof
 

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The air conditioner is a dehumidifer, so when the AC compressor kicks on, it is dehumidifying the air that hits the windshield. It is normal.
 

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The air conditioner is a dehumidifer, so when the AC compressor kicks on, it is dehumidifying the air that hits the windshield. It is normal.
Exactly! it's been the case with cars with A/C for decades, the front defrost runs the A/C too to help clear it faster, nothing new hear, move along, nothing to see/complain about ;-)
 

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Yeah most cars for quite a while force the AC on when the defrost is selected. Helps to defog quicker. The V is the first car I've seen that doesn't illuminate the AC indicator though.
 

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Yeah most cars for quite a while force the AC on when the defrost is selected. Helps to defog quicker. The V is the first car I've seen that doesn't illuminate the AC indicator though.
Do you mean the A/C is not on when you hit the front defrost button? It happens on my V as well but I find a way to turn it back on as it should be.

* Make sure the front defrost button is OFF before doing the followings,

- turn your key to ON position / press the start button to ON position,
- press the front windshield defrost button,
- press the air circulation button 5 times or more within 3 seconds,
- then you will see the blue light on the circulation button flash a few times,
- turn off the ignition,

Next time you start the car and hit the windshield defrost, the A/C will automatically come on.

Cheers
 

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Someone posted a similar question in another thread regarding the AC and defrost. I gave the same answer, but said that I didn't think that the AC could be controlled indepently. It turns out you can push the A/C button to turn off the light, but the compressor is going to continue to run as necessary to dehumidify the air no matter what the A/C button is set to. The whole point behind the defogging is to get the moisture off of the inside of the windshield.

Dehumidifying the air that hits the windshield is the best way to do it; therefore, the AC compressor needs to run some to accomplish that.
 

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Turn the fan off, crack the back window, this will cause a vacum, which will pull air through the intake infront of the windsheild and through your vents *free of charge* But everyone is right if you have your system running in the windshield or floor/defog setting the compressor will be working to remove moisture from the air.
 

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Do you mean the A/C is not on when you hit the front defrost button? It happens on my V as well but I find a way to turn it back on as it should be.

Cheers
No I mean that as far as I've witnessed, if you select front defrost the A/C is on regardless of whether the light on the button is on or not. Perhaps they decided to not illuminate the button because people turn it off thinking it will be cold air coming out? I've seen people do stupider things.
 

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It is like that on pretty much every new Euro, Asian car these days. As mentioned, the ac acts as a dehumidifier and draws moisture out of the air that causes the condensation to form on the glass.

There may be a way to alter its function though. My previous Hondas activated the ac when the defrost was on, but didnt illuminate the light. With a series of button pushes, it would permanently disable this auto ac function and the ac button would have to be manually selected to engage it.
 

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Discussion Starter #14
I guess my point is that the V's indiciator doesn't light up, and you can't opt to turn the A/C off in Defrost. You can toggle the switch and light all you like, it has no effect. I also thought it might be interesting to the hyper-milers out there that the A/C compressor maybe be on when you don't know it.

I beg to differ that all/every "new" car does this... Yes, I've had cars that turn on the compressor for you when you select a Defrost mode, but the A/C indicator is always lit, and you can always override it by pressing the A/C button to turn the compressor off. I have owned multiple BMWs, VWs, and Subarus (and at least one model of each with "auto" vs. "manual" climate control). I've also owned at least one Honda, Mazda, Ford, Chevy, Chrsyler... the "new" cars I've bought in the last 14 years (besides the V) for myself or my wife have been Mazda(1), VW(2), Subaru(6), and BMW(5). None of them did this, so I find it a bit odd :)

And for our Southern friends: Yes, the A/C being on with Defrost is good for dehumidifying the inside of the windshield. We Northerners and Canadians use the Defrost setting to melt ice on the outside as well :) And yes, I know that you can have A/C on and still get warm air out of the defroster, but it's usually not quite as hot for obvious reasons :)

Personally, I would prefer to able to periodically turn the A/C off when in a defrost mode, especially in the winter, because I don't want ice forming on my windshield, but after a while that dehumidified air really dries out my contact lenses ;-)
 

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I guess my point is that the V's indiciator doesn't light up, and you can't opt to turn the A/C off in Defrost. You can toggle the switch and light all you like, it has no effect. I also thought it might be interesting to the hyper-milers out there that the A/C compressor maybe be on when you don't know it.
As much as I'd like the control over it, none of the cars I've owned since about 1992 have ever had the A/C light on when the front defrost was on with A/C on in the background and all the manuals mentioned that this was the way it functioned.
 

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Point is many new cars have this function, maybe more CDN then US vehicles because both of my Hyundias, my Mini and the past 6 Civics all had this funtion.

Anyway, try this...

Turn the defrost on, push the recirc button 5 times. The recir light will flash a few times and it will then allow manual control of the ac during defrost operations.
 

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This automatically turning on of the AC when the defrost is selected is now sort of normal

Some manufacturers provide a way for you to override this, others do not

I used to worry about this all the time effecting my fuel economy, but I have since given up about worrying about it
 

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Baddog, I have an '04 Mailbu when in defrost the A/C is automatically on. If I turn it off it flashes a few times then lights right back up. Generally, I don't think the a/c units affect mpg near as much as they used to and they also disengage when you are at full or near full throttle anyway.
 
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