Defrost.

[punch]

Originally Posted by 07WYarisRS

All cars now days with A/C the A/C compressor cycles on an off when the defroster is on. When you select the heater the A/C compressor does not cycle off and on. They do this for several reasons, moisture control, circuulation, lubrication and keeping the system from freezing up complatly. And it keeps the compressors from siezing up from not being used in months of cold weather.
If you don't think this is the case, pop your hood, start the car and turn on the defrost and watch the A/C compressor. you will see it cycle on and off.
That's why using the defroster also causes you to use more fuel.

thats not what my owners book says.