04GTGuy

I know that running the A/C in general is going to cause your MPG to decrease. My question is does it make a difference in respect to MPG if you use A/C or Max A/C? I know the difference between the two, I just don't know if one causes more fuel consumption. Also, does it matter which fan setting you use (how fast the air is coming out of the vent). I have been told two different answers lately so I thought I would throw it out here and get it right. Thanks in advance.

-Chris

4600cc

Si. AC and MAX AC is different. MAX AC works the pump more. Speed of the fun does mattery but very little. Fan is electric and it puts load on your alternator, greater load equal more drag and less MPG, but this is very little compared to load by AC pump, this is so little in fact that it is negligible.


If you have an aftermarket ECU that you are able to tune 100%. You can take advantage of AC pump not running, because it means less engine load and you can run more timing and thus make more power.

pj1010

That wasn't really his question...and his post states that he does not have any aftermarket ECU.

I'm not sure, but this seems to be close to correct:

When you crank your car with the A/C off, it will idle at so-and-so (800?) RPM. Now when you turn on the A/C, the idle will drop a little, say 200-300 RPM, and recover. I would think that the only extra gas you are spending is enough to keep the car back at normal RPM. So...probably not too much.

Chopper

Running your A/C will cost you about .5 or less MPG.According to the 04 owners manual MAX A/C is more efficient than A/C.This is because the MAX A/C setting cools recirculated air and A/C has to cool hot air coming from outside the car.Once the air is cooled the A/C compressor shuts off and untill the evaporator coil pressure drops,stays off.The colder the air going over the evaporator coil the longer the pressure stays high,so cooling outside air heats the evap.coil and cycles the compressor more often.The fan uses such a small amount of electricity that I wouldn't worry about fuel consumption.You might consider fan motor replacement though.The bearings only have so many revolutions in them so the slower the fan is turned the longer it will last.Picking nits yes, but who wants to replace fan motors?I recently read an article in a ricer mag about synthetic A/C lube.They did a dyno test and did get a couple HP with the stuff.I looked for this miracle oil on the internet but must have forgotten some important piece of information as I haven't been able to find anything about it.

04GTGuy

Thank you for the replies.

-Chris