Most cars these days come with air conditioning as a standard feature – gone are the days when it was an expensive extra (for most of us, anyway). The HVAC system is an important accessory, and helps you stay cool in the car when it gets hot outside. However, the AC is powered by your engine – the serpentine belt that runs your alternator, water pump, power steering pump and other accessories also turns the pulley for the AC compressor/clutch. How the air conditioning system affects the engine Because the system is powered by your engine, it pulls energy from it during operation, which can have an effect on engine performance. You’ve likely noticed your car’s engine RPMs increasing at idle when the compressor kicks on. It does this to offset the power drawn by the air conditioning system. As to the question of how much power it draws, there’s no one answer, as it depends on the make and model, the engine, the condition of the engine and the air conditioning system and much more.