A different Air Con and FE question

[360cubes]

Originally Posted by *MAD DOG*

Ok, Who can answer this?

If i'm driving my car with the air con on and the fan on 4 does that use more fuel than if i have the air con on and the fan on 3, 2 or 1?

No. This would be the same as asking "By turning on all the lights will that increase fuel use as the electrical load is increased?" Again, No. As far as turning the fan on different settings to save energy, it will save electrical power by keeping the speed low, but will have no effect on fuel economy as the alternator is constantly charging the system. If driving around town, the engine might lug a bit while at stop lights if you run too much power through the system (ie. aftermarket stereo, etc).

It comes down to initial design. You should be able to utilize everything in the vehicle, such as headlights, 12V sockets with the AC on and fan turned on high with the brake pedal pressed (turns on brake lights). Vehicles are built to run all their required electrical loads without worry of stalling or having to put the transmission in neutral and give it fuel in order to sustain itself from stalling. The PCM can adjust fuel to compensate for above average loads and help boost the idle speed slightly to compensate. Sorry if I don't listen to or believe in CarTalk radio shows.


FYI: Don't forget that when you have the knob set to ANY defrost position the A/C compressor will run. This is especially important not to shut the vehicle off or turn it on when the selector knob is on a defrost setting. Turning it to vent or floor is the way to go, not to save fuel, but to save wear and tear on the system. The compressor is one of the largest electrical load devices in the vehicle. Keeping it off will aid in starting and overall wear and tear.

[*MAD DOG*]

Originally Posted by 360cubes

No. This would be the same as asking "By turning on all the lights will that increase fuel use as the electrical load is increased?" Again, No. As far as turning the fan on different settings to save energy, it will save electrical power by keeping the speed low, but will have no effect on fuel economy as the alternator is constantly charging the system. If driving around town, the engine might lug a bit while at stop lights if you run too much power through the system (ie. aftermarket stereo, etc).

It comes down to initial design. You should be able to utilize everything in the vehicle, such as headlights, 12V sockets with the AC on and fan turned on high with the brake pedal pressed (turns on brake lights). Vehicles are built to run all their required electrical loads without worry of stalling or having to put the transmission in neutral and give it fuel in order to sustain itself from stalling. The PCM can adjust fuel to compensate for above average loads and help boost the idle speed slightly to compensate. Sorry if I don't listen to or believe in CarTalk radio shows.


FYI: Don't forget that when you have the knob set to ANY defrost position the A/C compressor will run. This is especially important not to shut the vehicle off or turn it on when the selector knob is on a defrost setting. Turning it to vent or floor is the way to go, not to save fuel, but to save wear and tear on the system. The compressor is one of the largest electrical load devices in the vehicle. Keeping it off will aid in starting and overall wear and tear.

Thanks

[Castaway]

Originally Posted by 360cubes

......The compressor is one of the largest electrical load devices in the vehicle. Keeping it off will aid in starting and overall wear and tear.

I have to disagree with you; the fan, the compressor clutch, almost everything running on electricity get "disconnected" when the starter is engaged. So you're not lessening the load on the starter by turning things off. But i agree the more you use something, the more it wears