The A/C runs off a belt from the gas engine, thus, you only have A/C when the gas engine is running. However, there is a recirculation mode, where once the car is cool, the engine can go off and on as it wishes, and you'll see minimal changes in temperature for short periods like red lights. There is a control option to force the A/C to be on all the time, but then the gas engine is on all the time also.

Running the gas engine all the time, the special Atkinsen engine will still get you 7% to 10% better gas mileage with the A/C on full time.

Without the A/C, the gas mileage is 50% to 75% better than the regular Escape.
When I use A/C a lot, I get 33-34 MPG.
Without the A/C I get 40-45 MPG.

So, yes the A/C takes more gas, but the Hybrid still beats the pants off the regular Escape.

-John