A different Air Con and FE question

[*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?

[BailOut]

There is an unknown balance point between taking longer to move enough air to cool the car off (which uses more fuel as the a/c is on longer) vs. using more electricity to turn the blower faster (which uses more fuel as the alternator clutches due to the load, placing more of a load on the engine). The a/c compressor is by far the larger drain but the fan isn't free, either.

It is generally accepted that running at full cool with the fan on 3 or 4 (I find 4 to be too loud) until the desired temperature is reached is best, then either "pulsing" it on the downhills, or just as needed, rather than letting it remain on full time.

[UTVitz]

technically the answer is yes, this question has been addressed on a "car talk" radio show. Increased load on your alternator, a/c compressor may engage more often to cool the condensor, but the car talk guys said the amount of fuel used even over a long period of time was so small it was meaningless, you'd save more turning your car off at drive throughs if there longer than 30 seconds. Just know running your fan on high a lot will probably shorten the life of a very expensive blower replacement more than save some gas.

[1stToyota]

If you had automatic climate control I'd say it'd make a difference. If not, I doubt if reducing the resistance on the blower motor will cause you to use more fuel.

[Billstein]

If you had automatic climate control I'd say it'd make a difference. If not, I doubt if reducing the resistance on the blower motor will cause you to use more fuel.

I agree with 1stToyota:clap:

[1stToyota]

I agree with 1stToyota:clap:

Yeah, since we don't have any temp sensors in the cabin I don't see how blower motor speeds could ever play a role in clutch cycle time. More likely our temp blend door setting would make more of a difference, with maybe a temp probe or expansion valve on the evaporater core that would be tied in with the clutch cycles... :iono:

[360cubes]

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*]

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 :thumbsup:

[Castaway]

......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 :biggrin:

[billk]

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?

I say the a/c will run longer with the fan on 4, and this will use more fuel. This is because the faster the fan blows, the less temperature drop you will have across the a/c evaporator. so faster air will result in the air not being as cold, which means it will take longer to cool. I know this sounds stupid, but the slower the fan moves, the colder the air out the vent will be. So if the fan is on low, colder air will coming out the vent, which will result in the thermostat reaching temp faster, which will cause the compressor to turn off sooner.
I know on a hot day, fan on high cools the car faster, but lower the fan speed after a few minutes, and it will cool even faster.