I have a 1996 LS. Whenever I turn on the front air defrost, the air conditioner button lights up to blow cool air on the window. Is the front air defrost system supposed to work like this?

I'm fortunate to not have some of the more serious problems that some post here

 

yes. its supposed to do that. thats kinda how the front defroster works...

 

It does that because the A/C system dehydrates that air and dehydrated air helps a lot when you're trying to defrost a glass.

If it's humid out, blowing the humid air from outside will take forever to defrost the glass so it uses the A/C condenser to pretty much dehumidify the air.

 

Yup, that's not a problem. It's suppose to do that.

 

Solid. Thanks guys

 

Ive noticed the same thing AC comes on for front defrost (defogs window very well),
but I turn the heat on and the windows fog right up??
Just got the car and ive really only noticed this at night when it gets under 15 degrees celcius or so , but I want the car warmer...
hoping it wont do this when winter comes
I want heat but no foggy windows

 

Do you have the owner's manual? Never a fan of electronic climate control, but I'm grateful for A/C. Next time you want heat without foggy windows, try using the manual settings and choose bi-level or floor.​​​​​​​

 

Also, in the summer, if it is damp and/or humid outside, the A/C system needs to be on to remove fog from the inside of the windows. If it proves to cold for you, raise the temp into the high 70s or 80s. The A/C system will still be on and removing fog, but it will be comfortable feeling to you and your passengers. This is especially helpful if you get caught in a downpour running to the car and get in with damp clothes. If you have the A/C on at 70-75 degrees, it can feel chilly. Once you raise the temp up to 79-85 (A/C system on), the air won’t be so cool, but will still defog the windows!

 

Yeah Ive been meaning to read thru the manual (although its in japanese, so ill have to use google translate).
Its weird the floor setting with defrost fogs everything up too, that same button did what I wanted it to in my hyundai.
Ive tried every setting with heat and they all fog up
Ill try turning the heat up high with the AC/defrost on like you said might work...
Its exactly those cold, rainy days that I cant get the setting right, thanks!

 

Make sure it is NOT on recirculate—that will fog things up as well.

 

Oh ok wasnt sure about the recirculate button, thats supposed to be for best AC when its hot outside right?

 

Yes, when you get in on a blazing hot day and it is 125 in the car, make sure it is on recirculate. Turn the A/C on and the temp all the way down to LO. Crack the back windows a little and get moving. If it is raining out and/or the windows are fogging on you, make sure your NOT on recirculate.

 

Good info. My '97 LS400 defrost is not working (according to daughter)...gonna try these settings tonite and see if it works.

 

AC doesn't only cool the cabin, it also dehumidifies the air, or conditions it !
most cars have this as a automatic setting when the defrost is set, and I expect the LS to be no different.

even with full heat on, the AC can also be used to defrost or defog the windows, which is why the AC automatically turns on with this setting.
no cold air will come out but the air is conditioned so the fog dissipates.

@ colm83 the fog comes up only temporarily at the first burst of air but will eventually subside when the air is dehumidified usually within a minute or two.

 

I tried defogging with just heat and then the next day with ac on....huge difference in speed.