AC and Gas Mileage

Of course. When the compressor runs, it takes some engine power.

But if the compressor is running 75 percent of the time, or 85 percent of the time is going to mean extremely little in terms of gas mileage.

No. When you have the A/C on, the compressor is running pretty much all the time. If you set the temperature higher than the minimum setting, there's a heating coil in the system that brings the temperature back UP to the setting you want.

Paul

Interesting points. Now, I'm not sure of something:

When you tip in on the accelerator, from a steady cruising speed, does it curb or temporarily disengage the a/c compressor, as many cars have been designed to do, for purposes of 'giving the power back' to the engine?

I ran the A/C constantly in mixed city/highway (mostly highway) driving and averaged 30MPG in my 95 Accord 4cyl/Vtec.

So whats the difference if your hot and want the comfort who cares how much gas it uses.

Tom

The amount of additional gas used is proportional to the compressor "on" time and the outside abient temperature.

Professor

"twfsa" wrote

In fact, I have yet to notice any difference in gas mileage between a/c on or off in my '04 Accord 4-cyl auto.

As it would relate to compressor run time, yes.

The compressor run time is determined by the evaporator outlet temperature. As long as the evaporator temperature is above 33F. the compressor will run. Regardless of the setting.

Best fuel economy can be had by driving with ac off and windows up. Any time the ac is on, it costs gas, and is proportional to compressor on time. So the question is: how much do you like to sweat?

-- Tp,

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This is what confuses me about the discussion of AC relating to fuel economy. I have a 93 Honda Accord & I can feel when the compressor clutch engages & disengages. When it engages I can feel the engine is under more load(more vibration at stop or slight drop in acceleration or speed in motion). Surely fuel economy increases when the compressor is disengaged even with the AC "on". Thanks for your input. Rich

On the V8 engines a "properly operating" air conditioner will cause about a 1 to 1½ mpg impact in fuel economy in around town driving, slightly less with sustained driving at highway speeds. The operative phrase here being "properly operating".