2006 Tucson: question about defrost/defog

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Hello
5 years ago I bought an Accent GSi. I got it in the middle of winter, and I noticed that everytime I turned on the defog mode, the a/c light would come on. I got the dealership to disconnect that since I was
under the impression the a/c compressor sucks a lot of gas.
I just picked up my Tuc a few days ago and noticed it does the exact same thing. Does the a/c thing affect gas consumption when heat is blowing out instead of cold air? Can I disconnect this without having to go to the dealership? Should I not bother?
Thanks for your input
Alex
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cheg wrote:

Modern cars are mostly economical in the AC systems and do not use up the fuel like a generation ago.
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James wrote:

This same subject was discussed just a few days ago.
Untrue. The A/C dries the air, but that not only does no good when you're trying to clear the OUTSIDE of the windshield, it reduces the defroster's effectiveness. If you live up north, it sucks.
If you use the defroster to clear the inside of the windshield, then switch to heat once it's clear, the moisture on the condenser coils gets pumped back into the interior of the car and fogs up the windows again. For that reason, I prefer to use heat to clear the windows in the winter.
Having the A/C compressor running costs me at least 3 mpg in my Elantra. IMO, that's unacceptable for a "feature" that I don't even want.
Unfortunately, this is no longer something that can be easily disconnected. I contacted Hyundai about it when I had a nasty experience with it, but they had nothing to offer. In '04 and up, US market vehicles, the only way to get around this is to splice a switch into the A/C control line that comes out of the heater control module, so you can manually turn the compressor off. It's an inexpensive modification, but it requires removal of the dash facia and a bit of wiring. The switch I used fits where the cigarette lighter was. Since the car has an accessory socket, I didn't mind sacrificing the lighter to get better defroster function.
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odd I life up north.. and I have NO problem with that at all.. when in defog mode. ya just turn the temp up .. problem solved...
Pete...

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Pete & Cindy wrote:

If only it were that simple. I got into a situation in freezing rain where the defroster could not keep the windshield clear. Another 10 or 20 degrees in the temp of the air from the defroster would likely have made all the difference in the world. Canadian market Hyundai vehicles allow the A/C compressor to be switched off, which tells you something about the effectiveness of this dubious "feature" in cold climates.
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Brian..
oh, I forgot to tell ya, I AM FROM CANADA..;-)
Pete..

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Brian Nystrom wrote:

Something is seriously wrong then with your vehicle. I've never seen the AC consume even 1 MPG on a modern car. Actually, on my minivans and pickup, I can't even tell the difference between using AC and not. I check every tank MPG all year around and the extra gas used by the AC in the summer is lost in the noise of the MPG readings.
Matt
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Matt Whiting wrote:

Sorry Matt, but I'm not buying that and I've never heard anyone else make such a claim. An A/C compressor takes several horspower to run, which does impact fuel mileage. There is still a debate about whether rolling down the windows reduces fuel mileage more than using the A/C, but there is no debate about the fact that either one reduces fuel mileage.
Perhaps you do a lot more city driving than I do, where the mileage drop is less obvious, but a 3 mpg drop on the highway is normal.
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Brian Nystrom wrote:

I can send you copies of more than 10 years worth of MPG data...
I never said it doesn't consume extra fuel, and actually said just the opposite. However, you are talking about what a 10-15% reduction in fuel mileage? I don't know what your Elantra yields normally so I'm just estimating here.
In city driving, this amount of reduction is probably easily possible as the AC consumes about the same amount of power per hour, regardless of distance traveled. However, on the highway, this is a terribly high figure. Then again, maybe Chrysler and GM have more efficient AC than Hyundai. I know GM for years was the world leader in AC technology.

Actually, just the opposite is true. AC consumes roughly a constant amount of power per unit time. At slow city speeds when the vehicle is using less fuel per unit time, the AC consumption will be a much higher percentage of the total.
Matt
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Brian Nystrom wrote:

From my understanding, after the temperature drops below a certain temperature (usually about 32 degrees) the A/C compressor does not switch on in the defrost mode.
John
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JPH wrote:

That's what I thought too, but you can feel it kick in, both in the drag that it causes and the difference in the air temp. If it does cut out completely, it's apparently at a point that's too low, IMO.
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cheg wrote:

Sure, it affects gas consumption some as it is drawing power from the engine. However, most modern compressors are pretty efficient. I'd be surprised if it made 1/2 MPG of difference. And the increased defogging efficiency is worth it. Hitting something you can't see impacts your gas mileage a lot more than running the compressor for a few minutes. And once the windshield is clear, you often get enough defrost airflow even on the normal heat setting to keep it clear.
Matt
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This "feature" has been in place with most automobiles since the early '90s. However, the majority of vehicles disable the AC compressor below a certain temperature not only to protect the compressor due to low ambient temps, but also not to degrade the defrosting abililty. In my 1994 Dodge Grand Caravan ES it disables the compressor when the outside ambient temp is below 30 degrees F. The AC light is on when the outside temp is below 30 degrees, but the compressor is disengaged. I haven't tested this on our new 2006 Elantra, but I would be very suprised if this is not the case with Hyundai as well. Otherwise, all of us who own Hyundai's will be replacing AC compressors at a rapid rate!
Turning on the AC in the defrost mode helps the defogging ability of a defroster tremendously by removing the interior humidity. Assuming the disengagement of the AC compressor at low temps, this is actually very good engineering.
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Don Allen wrote:

That's true, but only IF you need it. It's not always necessary.

high enough temp to suit me. It definitely adversely affects the defroster's ability to keep the outside of the windshield free of snow and ice, especially when the temp is just below the freezing mark.
Additionally, I object to being FORCED to use the defroster this way. I used to use the A/C combined with the heater or defroster in my ex-wifes car WHEN I NEEDED IT, but you don't have the option to choose when to use it in the Elantra. Well, at least you don't in a stock Elantra. After the modification I made, I can control mine and use it only when it's beneficial.
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Brian Nystrom wrote:

Yes, I have noticed that my Sonata isn't very good at defrosting. Then again, it isn't very good at heating in general. The interesting thing is that both my 94 Chevy pickup and my 03 Dodge Grand Caravan have this same "automatic" AC in the defrost position feature, and they both defog and defrost exceptionally well. The Chevy is slower to start defrosting as it has a much larger cast iron engine that takes a while to heat up, but once warm it will make the water on the windshield turn to steam when you stop at a light.
Personally, I think this is more of poor HVAC design on Hyundai's part, than a poor idea in general.

Yes, I personally prefer to have more things manual than automatic, which is why I drive a stick shift. However, I have become used to having automatic timing advance, automatic mixture control and automatic fuel injection for cold starts... :-)
Matt
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Matt Whiting wrote:

It seems like a large part of the problem is that the fans are anemic. Position #4 in the Elantra doesn't blow as much air as position #2 in my old Excel did. The air gets hot, but it's not distributed effectively. I wonder if there's a higher output blower motor that would fit?

Sure. I have no objection to true advancements in technology, but it seems counterproductive to eliminate the driver's ability to choose how to use some systems. Like you I prefer to "row my own" gears and have never owned a car with an automatic transmission.
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Brian Nystrom wrote:

That could well be the case. Although, my old minivan (96 Plymouth) and my pickup don't blow a lot of air on the low setting either, but by the time I got halfway to work (about an 18 mile commute) I had to start turning down the temp setting unless it was below zero. I can drive the Sonata all the way to work on the highest temp setting and no be uncomfortably warm. My 03 minivan (Dodge Caravan) does blow much faster on all settings than my old minivan or my pickup. It gets uncomfortably warm in about 7 miles at any OAT above 10 or so.
I'm not sure a higher output blower is necessary as we can always use the higher speeds. I'm just used to not needing 2 or higher in most of my vehicles unless it is very cold (below zero) or very humid (car full of people with wet jackets).

Are you married? I never owned an automatic until I got married... :-( I did insist that my wife learn to drive stick, which she did very willingly. However, I've conceded to buy an automatic for the vehicles that she drives primarily and a stick only for those I drive primarily. Compromise is part of marriage, at least successful marriages! :-)
Matt
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Matt Whiting wrote:

Not anymore. :-)

Now that I think of it, I can only recall having one girfriend in the past 20 years who drove a car with an automatic. The rest have driven manuals. It's not like I planned it that way, but apparently I'm attracted to the type of women who prefer manual trannys, which I would categorize as independent, self-reliant and intelligent. Maybe it's just a New England Yankee thing...
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*** Update ***

would come on. I got the dealership to disconnect that since I was under the impression the a/c compressor sucks a lot of gas.

blowing out instead of cold air? Can I disconnect this without having to go to the dealership? Should I not bother?

Unlike my previous car, I found out this morning that I simply had to press the a/c to disengage it! On the Accent, you could press all you wanted on the a/c switch but it would always be on. Anyway, I'll be testing it in the next few days and keep you all informed.
Again, thanks for the replies!
Alex
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Elantra 02, and Santa Fe 03, they both work same way, push the buttom, A/C goes OFF.
It's a nice feature , here in Florida, were the humidity is always high, maybe not so much in the frigid norther tundra .....

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