[noflash]

The Auto button turns on the A/C, no matter the temp outside. I never did this before (unless clearing fogged windows).

I have just been letting the car do what it wants, but I wonder:

Is the A/C making the cabin more pleasant (with the heater)?

Is it unnecessarily affecting performance and fuel economy?

Opinions?

[F32Fleet]

Sounds like a programming issue. Unforuntately living in Atl requires me to have the A/C on almost year round due to our humidity.

[noflash]

Please for give me for posting b/f searching. Must've been out the day this was discussed.

Voltron gives the perfect answer.

Originally Posted by voltron1011

Your fuel consumption will be negligible with AC on during winter months. Even though the AC button is on that doesn't mean the compressor is actually engaged. The compressor engages based on a pressure switch inside the AC plumbing. Once the switch reaches a predetermined temp, it switches the AC off. This also takes into account humidity because the condensor takes water vapor from the air. The compressor will kick on just long enough to remove any humidity (even if it is -3 outside) from the air. This is why your windows won't fog up and your fuel consumption won't be affected.

[SCA]

It's normal. My car does it and the loaner I am driving does it. If the A/C is on with the heat is prevents the windows from fogging up. I usually turn the A/C off, but eventually I have to turn it back on because of the windows. I also turn the A/C off 2-3 minutes before I reach a final destination to dry out the evaporator from the condensation that collects inside of it. Over time you more than likely will get a mold smell from your A/C.

[combatcarry]

I think you should cut the AC belt. This will greatly enhance fuel economy.

Seriously... It is important for the AC clutch to cycle in the winter to remove humidity (as others have mentioned) and keep the compressor working properly.

The AC has kicked on during the defrost cycle on many vehicles for many years (even on my old '79 Chevy truck).

[pete_85]

it also has to do with mixing cold and hot air. If you leave the heat on you notice after a while it gets very hot and you have to keep adjusting it to your preferred setting again. With the ac on the climate is always balanced

[Laplacian]

Originally Posted by combatcarry

I think you should cut the AC belt. This will greatly enhance fuel economy.

Seriously... It is important for the AC clutch to cycle in the winter to remove humidity (as others have mentioned) and keep the compressor working properly.

The AC has kicked on during the defrost cycle on many vehicles for many years (even on my old '79 Chevy truck).

I was told by my dealer that the A/C system on the E90 is beltless. It uses an electrical motor to drive it. This (according to him) is why the BMW A/C is so efficient and doens't take anything away from the engine power. Can anyone else confirm this?

[kobechrome]

There's also an explanation in the owner's manual which I didn't really read but I'm sure it tries to explain it away....

[noflash]

Thanks for the replies. I am leaving it alone. The car is becomming smarter than I.

[dtelle]

??? i don't know any e-generator with enough power for electric AC compressor .

today the max power of a 12v generator is about 3kw ( available for all electric and electronis device in the car). a AC compressor need at leats this power.

[sdorn]

I read that the water pump and fuel pump are electric, but I am not sure about the a/c compressor.