My Mazda does it and I wouldn't be surprised if other cars do it. As it stands right now, when the A/C is on, the compressor cycles on for 10 seconds, off for 10 seconds. I think the rule of thumb is that A/C compressors can rob 15-20% of power from 4 cylinder engines. That's huge in a small engine. My Mazda 3 often uses 15% more fuel when A/C is on, compared to roughly 5-7% in my Honda Odyssey (with one compressor on).