Allright so when you run a/c your fuel mileage drops a bit right.

When I drive around I almost always have me heater set to the window defrost setting. I've heard that when on defrost your a/c is on. So does that mean when i have my heater set to defrost that my mileage is being hurt?

Also my ac dosent work anyways. Ill get it fixed when it gets hot out. So if my a/c dosent work but defrost turns on a/c would it affect mileage with it being broken?

 

When they say that your ac is on what I think they mean is, for instance my Neon, it cycles the clutch on the compressor and if you have a electric fan it turns that on. In the same instance it is not running the ac compressor which puts a extra strain on the engine in turn making it work harder and reducing your fuel mileage.

I probably explained this completely wrong and if so, sorry, but thats how I understand it to work.

 

If you have AC in a vehicle, running the defroster will cycle the AC. The reason fro this is to keep the condensation from forming on the windows, much like a fresh air setting on the dash. Have you ever seen a little import ( they are usually the worst) going down the road and the windows are all frosted on the inside? This is caused by not enough air circulation and the car actually being sealed to tight.

 

Since your ac doesn't work, I assume you mean the compressor is not running, so it shouldn't affect your fuel mileage, and you won't have the benefits of the defrost to remove the humidity either.

 

Actualy the AC drys out the air so you are not circulating warm damp air on to the wind shield thus having moisture forming on the inside of the car,

 

Yeah, the A/C's dryer. And if ur A/C doesn't work, you could always short belt it if ya really get picky about mileage, one less pulley to turn. Especially if the A/c is bad b/c the clutch went out or something, it could be dragging a bit.

 

Ya I dont know if the compressor works or not. I have never had a vehicle with working a/c. All that I know is it dosnt make cold. I plan to see what kinda bill I will be looking at to get it fixed in the summer. Im not really concerned with if its losing me a bit of fuel mileage or not, I was just curious. Thanks

 

If your compressor clutch is functioning you should be able to hear it engage (at idle) My system is not charged therefore "doesn't work" but when I turn it to ac or windshield defrost it cycles on and luggs the motor a bit. Regular heat settings shouldn't cycle the AC, but defrost does usually( haven't seen the auto defrost/ac in all cars). You can look at the compressor while its running to see if the clutch engages. Even with poor charge, the system still has pressure and will tax the motor if its spinning. If your worried about MPG and the clutch is functioning do like Nick02ram said and put on a shorter belt to bypass the compressor. The reduced rotating mass will free up MPG as well as some pony's even if they are Shetland's! Hope this helps.

PS. AC is a refrigeration process which removes heat and moisture form the air as opposed to an evaporation cooler which works by evaporating water into the air. (lick your arm and blow on it, gets cold don't it)

Thats my two cents

 

This is kinda off topic but I saw on myth busters that they proved "during the hot weather at least" That running the AC didnt affect fuel mileage as much as driving with both windows down. Due to the added drag caused from windows down. Know this is not what you were asking just though I would throw that in.

 

they do some interesring stuff on myth busters. I likked the one where they tested replaceing a fuse in an old pickup with a bullet.

 

Who used to do that? See if it'll explode?

 

The myth was about some good ole boys out in the woods after dark and the headlights died, so they changed fuses with a .22 LR cartridge, and then got shot in the crotch, mythbusters got it to go off but "Buster" the test dummy received no penetration. It was the casing that had the most velocity not the bullet. Still wouldn't recommend it !

 

i WOULDN'T DO THIS EITHER

 

the casings also were the projectiles in the bonfire/bullet test because the casing is so much lighter