02 Corolla MPG with/WO AC on

Actually, the person who said that was talking out of his ass, as usual. He'll stumble along shortly to do that again.

Cooler air is denser, and less fuel is required as a result.

Until we get the well-intentioned government mandated ethanol added, then the mileage gets worse again. Not sure if that's kicked in yet.

got that one backwards.

OOPS, my bad. I had the right idea, but backwards.

The comparison in fuel economy with the AC on and the AC off has to be in the same environmental and operating conditions and the same fuel top be valid.

In cooler weather, the engine coolant takes longer to reach operating temperature. The electronic controls delays automatic transmission shifts until the coolant reaches a target temperature so that the engine warms up more quickly and reduces emissions. While the transmission upshifts are delayed, fuel economy suffers.

Even heated O2 sensors take longer to reach operating temperature in cold weather than in warm weather, and until the O2 sensors reach operating temperature, the engine electronic control unit remains in open loop operation, which is less fuel efficient than in closed loop operation.

Fuel companies change fuel formulations with the seasons, which may have a positive or negative result in fuel economy.

Another difference in the effects of the AC on fuel economy is the output of the engine. If the engine has more horsepower and torque, the AC compressor's drag has less effect than on an engine with lower output.

Heavy use of electrical accessories can also have an effect on fuel economy. Using lights more during the shorter days, rear defoggers, high amperage stuff on the cigarette lighter, seat warmers, etc can add up on the alternator load.

All these variables makes an AC on or off comparison during different operating conditions invalid.

Fuel economy tends to suffer during cooler weather mostly because of a variety of factors other than AC. For example, fuel economy will probably be better in the same weather conditions in the spring than in the fall with the AC off.

The effect of denser air on fuel economy with an electronically fuel injected engine is difficult to quantify with different operating conditions as well. Air density should affect the system's mass air flow (MAF) or manifold absolute pressure (MAP) sensors, which tell the electronic control unit how much fuel to inject.

Which is why Mythbusters did it the way they did it--the right way.

All I kmow is that we get 2-3 MPG more with the AC off, it's quite clear.

no, what you know is that you get more MPG when you don't use the AC.

That's way, WAY different, as Ray pointed out.

Driving with the system on recirculating mode is a catch-22. The recirc mode does not recirculate all of the air, some outside air still enters the cabin. In recirculate mode, moisture and CO2 from the occupants breathing could build up more, causing the inside of the windows to fog, so the AC has to be used more to defog the windows. The other drawback to using recirc mode all of the time is that the heater and evaporator core will tend to build up mold more quickly, causing a musty smell and possibly reactions to people with mold allergies, which is why the automaker recommends using the fresh mode most of the time.

If you use the recirc mode most of the time, I recommend that you use BG Frigi-Fresh 2 or 3 times a year to keep the HVAC system from getting to musty.

Just curious... Do the outside fumes and pollen bother you when you are walking down the street? If the effects are worse in the car than when you are walking down the street, try the fresh mode most of the time and use recirc when you are behind a bus or diesel truck.

Not so much here in Denver. Maybe Japan? Miami? NYC?

If we could only get "fresh" air outside, eh?

Play musty for me? :)

I take antihistamines year round, but yes, some. Depends.

Ahh...

You do get fresh air outside. As Ray says, the car's systems require fresh air to prevent mold from forming.

That YOU don't consider it to be fresh enough for your dainty constitution, is immaterial.

You've never sat in a Denver traffic jam?

In this area that's just silly.

We had 6% humidity and 75 degrees 2 days ago. I just got popped on the breast with static getting out of the car.

Again, not living in Japan or Miami.

You've never sat in a DC traffic jam?

So how do you think that there's "fresh air" coming in, when there are cars in front of you?

And yes, if I COULD, I'd seal that passenger area tighter than a drum and have my own oxygen supply, if possible. Hmm, I wonder if putting a tank of clean compressed air in the car... nah, too expensive.

I understand the sealing isnt perfect as I'd like, and that some "fresh exhaust fumes" will get it, but I sure dont want any car mfg allowing any in on purpose when I close the vents.

It's just like the issue of them turning on the A/C when I put the heat on the windshield. I dont want Big Brother, whether it's the damn government or the people who sell me my car, controlling my life. *I* want to control my life. I think that *I* am more qualified to make decisions for myself than THEY are.

So wire in a toggle switch to cut out the AC compressor.

I'd have to have someone cut the compressor wire off the vent switch?

The compressor could still be turned on, IF I wanted it, with the push button that does it anyway, right?

So is it a matter of cutting the wire off the vent switch, or does the computer do the deed?

While they're cutting wires from the vent switch, maybe they could also cut the one that opens the vents when the heat goes on the windshield. Or is that under the influence of the computer too?

Not necessarily there.

It's a simple circuit interruption, with the switch closed the AC functions as the factory designed it, with the switch open the compressor doesn't run regardless. -That- gives you total authoritative uncompromising supreme command of the AC compressor.

It doesn't matter if the computer does the deed, it is a simple circuit interruption.

That would take me studying the circuit diagrams for your vehicle which usually doesn't come free. I do honor Paypal...