Effect of A/C on MPG

[kaiser]

Originally Posted by roverbarmy

Cheaper than driving with your windows down and ruining the aerodynamics!

I have heard that before, but I have never seen it proved. There is a noticeable effect on the engine when the AC is switched on in some cars. You can actually feel the engine being loaded as a "jolt" to the car.

I don't know what the extra power consumption is, but a couple of kW would not surprise me. The effect required to propel the car against air resistance is highly depending on speed, and aerodynamics. I am not sure how much the aerodynamics get degraded by opening windows however. Not noticeable at lower speeds, I would guess.