I can pres the MODE button until the arrows on the display point up at the winshield indicating DEFROST. If this is the case, why (and what is the purpose) for the front defrost botton to the left of the MODE button?

 

To turn on the a/c compressor

 

It also saves you having to cycle through the choices. Turn on defrost, then hit it again and it goes back to your previous settings.

 

Convienience. That's the only reason for it.

Anytime you select the floor or the defrost vents (or any combination that includes them) the AC compressor will cycle.

 

if you want to defrost the window like the car does it, you would have to do the following :

Hit Mode till you get the front window selected, switch to 'fresh air' not recirculate, and activate the AC.

Its much easyer to just hit the defrost button and hit it again, I dont want to fumble with a lot of buttons when im going down the road at 50 and visibilitys is getting more and more limited from the fog on the window :-)

 

50?? you mean 80 right, cause it just feels like 50

 

In most other cars I have been in, as soon as the defroster comes on, so does the a/c compressor, but the reason behind that was so the compressor seals would not start to leak from lack of use over the winter. If it was not for the defrost button, turning the a/c on would not be a requirement to defrost the window.

In the summer, it's the fresh air that defrosts the window, and in the winter, the warm air. At least that's the behavior of Canadian air :p

In my experience, the compressor does nothing because I have also had cars without a/c the perform just as well as cars with a/c (no difference).

 

The front defrost switch is there to satisfy FMVSS 103. Required to have a specific marking on the HVAC control panel to initiate windshield defrost. Cycling through the "MODE" functions would not satisfy the requirement, although it does the same thing.

 

One of the side effects (and benefits) of running the A/C in hot weather is to remove moisture from the air. Running the compressor while in defrost (actually de-fog) mode can aid with this. Also, even during cool or colder times you can run the compressor even with the heat on to prevent window fogging to begin with - as long as you have a "foreign" car that has a distinc control for the compressor.

While making folks turn on the compressor does help the seals "in theory" they do it for the maximum and quickest defogging.

Dennis