I have a 2001 Civic LX sedan and when I turn on defrost, the A/C button light goes on and won't let me turn it off (it also sets it to outside air, though I can turn that back on). Even when I switch it away from defrost, the A/C stays on (though I can turn it off manually at that point).

I've never driven a car that turned on A/C when I turn on defrost, and it seems counter-productive to run cooling when the heat is all the way up. It also seems buggy to not allow me to turn it off, then keep it on when I switch it away from defrost.

Is this how my car is supposed to behave? I'd rather get a response here first then just take it to the mechanic as I haven't found anything easily online that explains this.

 

Typically you want the AC on when running the defroster as it dries out the air, which is what removes the fog on the windows. Otherwise you are recycling the same moist air that caused the fog in the first place.
Many older cars don't allow the AC to be off in the defrost position. I would think the 2001 one would allow it, but it is possible that it won't.
I am sure someone with a 2001 will chime in with a confirmation of the correct answer.

 

That's all fine and dandy then, but I don't understand why it leaves the A/C on when I switch from defrost to any non-defrost setting. Is that how it's supposed to work? It's more driving distraction or I forget and wonder why cold air is being blown in during a snow storm in the middle of the night.

 

Can't really say. Depends on the type of AC selector you have. On mine (94) the AC button is in or out. If yours is a momentary switch, then it is possible that it could default to on. Hopefully someone with your year of car can chime in with better answers.

 

the ac should not stay on when you switch from defrost to non defrost settings on any 01-05 civic there is something wrong with your system. but you do have the ability to de-activate the ac function while in defrost mode


1) Have the car turned off.

2) Turn the "air condition position" **** to the left all the way (counter-clock-wise).

3) Hold the "air-recirculation button" and the "A/C" button "DOWN". (don't touch the "defrost" button)

4) Start the car with the "BUTTONS" held down, and wait for 7 seconds.

5) All done. You can turn the "A/C" off and on now.


P.S. To turn the original feature back on, repeat all steps, but for "STEP 2", turn the **** all the way to the "right" (clock-wise).