Little different for the 2002 and newer models. I have a seperate button for electric defrost which includes outside mirrors, and windshield(via electric mesh), and also if you turn the selector **** to (defrost / lower), yes it will route the air upwards but it also automatically runs the a/c to take the moisture out of the air blown onto the windshield, otherwise you'd be getting ice forming on the inside of your windshield.

 

No ****. Have you ever opened up the HVAC box before?

But the A/C compressor WILL kick in when the heat is on.

 

I have that button, too, but I doubt you have an electric mesh in your windshield. That is usually reserved for back windows. And why would you get ice forming on the inside of the windshield when you can simply turn the temp to warm? Sometimes, in Florida, we need the A/C on in defrost mode or the windshield will stay fogged from the humidity.

 

There's an HVAC box on these trucks? Do you even know what HVAC stands for?

You sure about that?

 

The A/C Compressor kicks on on mine when it is in defrost mode only. Any other time and it's not cycling.

 

all it does in my truck is divert the hot air from ducts on dash and floor to ducks on dash? nothing else kicks on and there is no more draw from ac compressor.......Of course up here we only use defrosters with heat so....
I guess I could see the ac kicking on if it selected to cold and defrost for areas like Florida.
and yeah I was thinking I never heard of a windshield with electric wire heater defroster in it....antenna wire yes...heater no..

 

Actually, the purpose is two-fold for the AC to kick on when the Defroster is activated:

1) It helps draw moisture out of the air, and

2) it allows the AC system to circulate the coolant and oil that it contains so that the seals don't dry out.

 

Excellent.

And yes, if you don't take the moisture out of air(aka when your defrosting), on a freezing cold windshield(aka winter), the air from the duct will turn into ice on your windshield.

And yes, my windshield has defrosting mesh on it. If it makes a difference, I have the SLT Plus Laramie edition. It contains, power seats, power pedals, power windows/locks, auto dimming mirror, two tone leather seats, black interior with cherry wood, overhead computer, electric 4x4 switch, dual climate control, heated seats, infinity stereo, it even has a plug-in heater for the engine(which is not diesel), and much more. you can also find windshield defrosting mesh on newer ford's.

 

All of this talk about heat is making me remember that I need to figure out why my air flow both cools and diverts to defrost when on floor setting regardless of rpm or engine load... Hmmm must search this when I get home from the commute.

 

Just lookup the diagrams from dodge.