2004 Ford Expedition Connection between Gas Pedal and A/C

The vents are run by vacuum. When you push on the gas, vacuum drops in the engine. My guess is there is a vacuum leak between the engine and the panel in the vehicle that determines where the vacuum goes. Check under the dash for loose or broken hoses. Also, check under the hood of the vehicle. Sometimes, with the engine running, you can actually hear a hissing sound from such a leak, so you may want to try that.

Let me know what you find.

Joe