AC/Defrost

[Kaderabek]

OK, why does the AC turn on in my non-climate control 97 when I switch to defrost?

Brrrrr......

Thanks,

TJK

 

[MrZumma]

The A/C removes moisture in the air. The drier the air, the less moisture there is to condense on the windows. With just the heater running, you are only evaporating the moisture on the windows, not removing it.

 

[DRTDuck]

yes to what Zumma says. in my 96, the AC doesn't automatically come on with the defrost, however, if there is a great deal of moisture and the windows are fogging up, i push the AC on for a couple of minutes, and it dries the air right out

 

[Kaderabek]

OK, understood, with some caveats. First, what's the difference between evaporating moisture and removing it? Once evaporated, it's removed. I guess you could remove it without evaporating it, like with a towel or something, but as far as the defrost function goes, it's either evaporated or there. Evaporated equals removed?

Also, another function of the defroster (de-froster) is to remove frost and/or ice by warming the windshield. The AC being on isn't going to help that function at all.

I'll read the owner's manual tonight, perhaps this feature can be defeated.

Thanks!

TJK

 

[MrZumma]

Once evaporated, it's removed.

Not quite. Once evaporated, the moisture is still in the air. But when it is removed, the moisture collects/freezes on the evaporator and as the A/C cycles on/off, it will melt and that is what you see puddling up under your vehicle on a warm, humid day. The moisture you see under the car was moisture that was in the cabin of the vehicle..

Here is a link on the theory of A/C...

 

[MrZumma]

Also, another function of the defroster (de-froster) is to remove frost and/or ice by warming the windshield. The AC being on isn't going to help that function at all.

I'll read the owner's manual tonight, perhaps this feature can be defeated.

Thanks!

TJK

True until the A/C part. The A/C will then remove the moisture, not just evaporate it.. Warm dry air will do a better job at clearing an icy/frosty windshield than hot/moist air... Even with the A/C running and full heat selected, the air will still be very warm and will work much better at removing the frost/ice from the windshield.