ok so this is prolly gonna sound like a really stupid question, but me and speedracer89 got into a extremly heated debate over this. so here it is. he thinks that if u have ur defrosters on, you will get less gas milleage then u would if u didnt have them on. I think that he has no clue what he is talking about, cause ur defrosters are no different then ur heat, and ur heat just uses the heat of the engine that is already there. so i was hoping u could settle this discussion and put one of us in our place lol.
your started an argument over defrosters?
jesus you need to get out more.
Blower fan running = more draw on the electrical system = slightly lower gas mileage
I believe when you turn on your defrosters your A/C actually turns on. It does that because the A/C will take the moisture out of the air and therefore defrost better.
that would depend on the car.
If the AC does turn on, it will lower your gas mileage. If it doesnt, the current draw from the blower motor alone will not make a measurable difference.
every car I know uses the A/C for defrost. A/C will make a big difference in mileage… defroster grid on the back window will make a small one.
Either way it makes a difference.
almost every car in the world ac turns on when you turn the defroggers on…
and that would indeed be less gas milage…
:tup:
you are not a mechanic…
switches are ground side controled… KOEO the blower motor is HOT…
the switch on a blower motor is a ground side control, no difference in “electric draw”
older cars do not. cars without AC obviously do not. without knowing the car in question its stupid to argue about it.
actually its a stupid thing to argue about anyway.
rear defrosters don’t use a blower. they run current through the grids on the glass.
Huh? Are you saying that a spinning fan does not require more energy than a slower or stopped fan?
wasnt there a Myth Busters on this
Who really cares, they are kind of necessary regardless. 
Technically though the answer would be yes regardless of the circumstances. The biggest being if the car is A/C equipped, but even then the electrical draw would have some difference though not noticeable.
My 05 GTO does not automatically turn on the A/C for any setting of the defrost. If you want to use the A/C for defrost you simply press the A/C button. Much better than automatically turning it on when not needed IMHO.
Would you please just stop posting in technical threads.
most cars use the ac condensor to DRY the air, so that it will defog your windshield faster.
Works along the same principal as a dehumidifier.
Otherwise you would just be pumping hot humid air at the window, which won’t do as good a job.
The AC doesn’t come on in my VW when I’m defrosting. Granted, it also doesn’t come on when I press the AC button… 