Many new cars will turn on the A/C by default as soon as you turn on the front window defrost. My '92 rodeo doesn't, but my '03 Sierra and '02 Civic do.

Not only that, but there is no way to turn it off. I have to change the selector to the floor or something, then I can manually kick the A/C off.

Steve

True, but most if not all vehicles have a thermostat of sorts that disables the AC function below a certain outside temp...certainly above the stated temp of 5 degrees F.

I've got five bucks that says if you have a nose, you can't miss the smell of anti-freeze in your passenger compartment. <img src="/forums/images/graemlins/wink.gif" alt="" /> It's one of the sweetest, most pungent smells you'll ever run into. Ranks right up there with the sulphur smell of a burning catalytic converter, or that horrible smell of women's perm solution you've all gotten a whiff of while walking by a salon in a mall somewhere...

-Chris

Then use taste...don't *drink* the stuff, but wipe your fingers on the underside of the dash at the firewall, around on the carpet etc, etc. Put the tip of your finger in your mouth and you will very easily taste if there is AF at all. It will be a very sweet taste.

You can also try this when the window fogs up. Again, it should *smear*, and you should get a faint taste as well.

Steve

I'll pass go and collect my five bucks <img src="/forums/images/graemlins/smile.gif" alt="" /> Because I can't smell that stuff for nothing. My wife has smelled antifreeze and asks what it's from and I'm looking at her like what are you talking about? She'll be wrinkling her nose and I just don't smell it. Now the perm solution, that stuff makes your eyes water <img src="/forums/images/graemlins/shiner.gif" alt="" />

Not true on the defrost function. Take a poll and you'll be surprised at how many people are ignorant on how the compressor works. It's like when a car is running hot, I'm surprised how many people don't know to turn OFF the A/c compressor, crank up the heat, and roll down the windows to prevent overheating.

The average person isn't educated enough about cars and A/C to know it just turns on a compressor. They definitly aren't smart enough to know it pulls moisture out of the air, or that it can run with the temperature set either cold *or* hot. (Which is why more and more vehicles are getting rid of the button and just putting on a temperature dial).

Thus, the average person *might* be smart enough to know they could use it to defrost in the winter, when it's cold. But they wouldn't think to do it when it's warm out.

I hate to tell you how many cars I see in DFW in the spring and fall at the stoplights, windows down....and the telltale A/C drip. And I know some of them have the compressor button.

I'm not criticizing anyone on the board, or singling out any nationality. As vehicles got more complex and dependable, people just don't care to learn new things. The electronics and "bling bling" is much more interesting--there's more of an "entertainment" payoff factor learning how the Dolby Surround Sound and DVD player works than understanding the A/C. And there's reality shows to watch and video games to play, much more entertaining than learning mechanical car operations.

As an aside, one of the "evil crusadings Texins" died last week....he rejected textbooks for the state (which affect the nation) because they had 20 pages of Marylin Monroe, and only one page on George Washington. And you expect people to know how heat transfer works in the car?

Um...what is "not true" about my statement? <img src="/forums/images/graemlins/confused.gif" alt="" /> Because it is absolutely true for three of the last four vehicles I have owned, and the fourth one I never bothered to find out.

Below a certain temp (probably at a different set point for each maker, cartainly below freezing), by design the AC does not engage in the defrost position because there would be no point. When the dewpoint is below freezing the evaporator simply cannot get cold enough to remove any moisture.

In warmer weather, then yes the AC does engage for defrost.

I was just kidding with the 0w-30 oil.

Does your defog work when it's cold? Cold air (with you inside breathing warm moist air) is not efficient at defogging a window. Dryer air works better. My parents Olds, I know it clicks on.

I've got a Ford Tarus now and I bought it in becuase the windows were down on a cool day, and even with warmed air blowing in, the compressor wouldn't shut off. I thought it was broken. According to the dealer (who might be lying), that's how it's designed. I wasn't happy with that, but at the same time not upset enough to wire in a switch.

Obviously, different experiences with different cars means they're set up differently. Given the new Rodeo (not much of a data point), I think Japanese manufacturers still keep the A/C (compressor) button in, and assume you are smarter, while American car companies assume you are dumber. Age of the vehicles is also a factor--your last four cars; were they all from the last three or four years? They might also vary it by model. A newer, more expensive vehicle with a digital temperature setting will probably have a fully computer controlled compressor, while at the same time running the compressor no matter what when the defog is on.

Wayne, you're obviously not even reading my statements, because nothing you are saying negates what I said.

One more time: on most vehicles the manufacturers design the defrost system so that the AC compressor DOES NOT come on when the ambient temps are well below freezing. Above freezing, the AC compressor DOES typically come on to remove moisture from the air (though as you have stated on some vehicles this is optional with a separate AC button).

Which brings me to my main point (again): Since the original post was talking about ambient temps of 5 degrees F, the discussion of the AC compressor and defrost function is MOOT.

Since you're a Texas boy, we'll forgive your ignorance of bitter cold temps... <img src="/forums/images/graemlins/pfft.gif" alt="" />