Why does the AC come on when I use Defrost? - Honda Prelude Forum

x97tmp · 01-29-2002, 08:34 AM

Hey,
I've noticed that when I've got the heat blasting on my feet and then I switch to the defrost, the AC light automatically comes on. Is there a reason for this? I usually turn of the AC right away, but I was curious to know if this is suppose to happen and if so... why?
And if not? should I try to stop it from coming on.

thanks

Rukusracing · 01-29-2002, 09:06 AM

Have you ever tried defrosting your windows, and it just doesn't work with the heat. So you try cold air, and that doesnt work, so then you put the heat and defroster on with the air conditioner, and magically, it defrosts! Well, it just so happens that the conditioned air helps defrost the windows, so now car companies decided to turn on the AC automatically for you when you put the defrost on so you don't have to. So don't worry, you don't have anything wrong with your car!

YVR_98Prelude · 01-29-2002, 09:46 AM

The A/C dehumidifies the air which in turn helps clear the windows quicker.

Rukusracing · 01-29-2002, 11:49 AM

There ya go..........

Dragazn · 01-29-2002, 01:12 PM

On the side note, doesn't matter if you have it on heat or not even on cold it wil turn it on if you point it to the mirrors

x97tmp · 01-29-2002, 01:27 PM

I can see how that would help defog the window... but lately with winter and all its mostly been ice on the outside of the car that I'm trying to get rid of...
not the humidity on the inside of the window

DirtyLude · 01-29-2002, 03:08 PM

Pretty much all cars do this now. The Prelude is the only one I've seen that allows you to see the the A/C is actually on and disable it. My MP5 I have to break open the climate control panel and modify some wires so that it doesn't turn on the A/C everytime I turn on the defrost.