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Air Conditioning and Gas Mileage

I’ve heard that fuel consumption increases when the air conditioning is engaged. I believe the reason cited is that the air conditioning increases the engines rpm.

Today I engaged the air conditioning while driving at 100 kms per hour and there was no discernable change in the rpm. What is the truth concerning this matter?

I apologize. I just noticed that this question has recently been addressed (see “air conditioning/ gas usage”)

Air conditioning increases the load on the engine, and if you are sitting at idle turning it on will also increase the RPM to compensate for the extra load, but once you are traveling down the road the RPM is directly related to your speed and what gear you are in. So, yes, AC will very slightly increase your fuel usage because it requires some power from the engine. RPM is not directly related to the AC being on.