AC on when Vent to Windshield

[freeyellow2000]

Whenever I use "defogger" to windshield, the AC light turns on automatically and i can't turn if off unless I the move selector to something else beside the windshield (ie to floor, cabin....)


97 Camry LE (manually climate controls)

I remember see a thread about this but I can't find it?

How to I turn this off?
And how to I turn it back on?


PS. I have a debate w/ my brother are you suppose use the "Cold" or "Hot" to defost the windshield.....also are your windows open or closed

Situation: Driving at Cold Night 32-60F

Would it be cold because .... your breath is source of the heat causing it to fog up? but It defeats purpose and it would make the interior cabin even colder then it is already (epecically with auto AC turnning on)

or Hot so the outside air and the interior air will not be able to condesn (sp)on the windshield


Situation: Same as above with hard pouring rain? What are you setting going to be?

[lucanhookup]

same problem i have when ever i turn on my heat to the windshield the a/c turns on i dont remember if it didnt before but one day i notice and it never turned of unless i put it in another set i hate that crap

[99camryLE]

On all modrn cars he AC will automatically turn on when defogger is used. The reason is that windows clear up quicker using fresher air, and supposidly A/C provides fresh air.
As for the temperature, keep the dial directly between hot and cold air (50% hot and 50% cold) and at full blast with the A/C on to clear the windows up the quickest.

[lenjack]

Right. It's deliberately designed that way on newer cars. It will defog much faster that way. It's not something you can change

[amerikim]

Actually windows fog from moisture in the air.
What airconditioner does is it takes moisture (humidity) out of the air.
If you do want your windows to clear fast, wind the windows down if you don't mind the cold.

[Gen3cruiser]

On all modrn cars he AC will automatically turn on when defogger is used. The reason is that windows clear up quicker using fresher air, and supposidly A/C provides fresh air.

AC provides fresh air? An open window provides fresh air.

Air conditioning clears up fogged windows because air conditioners compress air and REMOVE MOISTURE. The "dry air" that comes out that was air conditioned when blown against the fogged glass picks up the moisture and puts it back into the air.

[Toysrme]

On this '93 lexus, if you use defrost, or leave the climate control to auto it will use the defogger.


All cars default the A/C on if you are defrosting. By blowing dry air on the windshield, it eliminates moisture(foggy) on the glass much quicker.

[CraigW]

Yes, The big 3 finally won out and the compressor now engages in certain modes. I have found that there is plenty enough air in "floor" setting still reaching the defroster vents up top. So I dont turn mine past "floor" I use heat and crack a window or two as well.

Yes, the use of the compressor will clear the windshield very quickly. But I have found that later things seem to be worse if you have allowed it to engage. After you turn off the car and let it set the moisture problem is worse IMO. I clear my windshield without the use of the A/C system.

[GaviN]

My Altima does this also. I hate it because it bogs down my car between switching gears and I hate that. I hate not having control over things like that

[virtualkuz]

in my 05 XRS I can pick whether or not the A/C is working on the two defog settings. I was pleasantly surprised because usually whenever you put the defog on in cars the A/C automatically comes on. Without the A/C on it is slower to defog but it still works well.

Another thing to consider is this:

If you don't use the A/C at all for the 3-5 cold months you have the whole system just sitting there. In the R134a lines there is also oil to lubricate the compressor. It is never a bad idea to run the A/C in the winter just to get the system operating and move the oil around. Seized A/C compressors are an expensive replacement $500+

[99camryLE]

Originally Posted by Gen3cruiser

AC provides fresh air? An open window provides fresh air.

Air conditioning clears up fogged windows because air conditioners compress air and REMOVE MOISTURE. The "dry air" that comes out that was air conditioned when blown against the fogged glass picks up the moisture and puts it back into the air.

That makes more sense. I read the fresh air thing in some car magazine (Car and Driver I think)

But have you ever cracked open a window to defogg the windsheild or any other windows? It works. Next time your windows are fogged up, crack open all four of your windows, and they'll defogg on their own. Not trying to be defensive, just stating a fact.

[YESCA]

If you leave the dial on heat, it will warm up, I guess what I am trying to get at is what is the big deal? BTW the defrost takes moisture out of the air like a dehumidifier.