I'm not sure with the HHR. However I have drove other four bangers that did that. When getting on the highway it would kick the ac off so you had full power.

I don't remember reading that in the SS manual (I have CRS though ), but I know the wifey's S4 disengages the AC clutch under heavy loads.


I have the RPD set to show fuel pressure and just popping the rear of the sunroof will raise it 50 psi or so at highway speeds.

Most cars will kick the AC out at wide open throttle. Also most cars will add a a different tune when the AC is on. Often it will add a little fuel to compensate for performance and idle.

Suppose that where the drop in gas mileage goes then?

Well think about it. It takes more HP to run an AC unit and more HP = more air and more fuel.

If fuel and more power were not added you would feel more of a drop.

This is nothing new as I could always see a similar change in power and MPG in even the V8 engines. In the past it was even worse when all you had was a selinoid to bump up the throttle on the carb in the pre Fuel Injection days.

Alts, Water Pump, Converters/drivelines, Power Steering, AWD, etc all take power away from the car to run. This is why we have electric power steering that was orignally developed for the Fiero. Once it was canceled they found it to be useful in gaining more MPG.

In the old days 1970 and before they used to rate engine HP as Gross HP with engines stripped of everything on the dyno. 71 and later they went to Net HP and it is an engine fitted with the accesories. That is why some of the engines from the 60 had so much power and only ran 14/15 seconds. It was not only the tires that limited them. Todays engines in Gross HP would have some wild numbers under the old system.

Hyper, how do you explain that??

the new chevy cruze shuts off the ac when you step on the peddle and turns it back on when you let off. its to free up that extra hp