2004 Buick Rendezvous Owner's Manual - Page 177

You may notice a slight change in engine performance when the air-conditioning compressor shuts off and turns on again. This is normal. The system is designed to make adjustments to help with fuel economy while still maintaining the selected temperature. On hot days, open the windows to let hot inside air escape; then close them. This helps to reduce the time it takes for your vehicle to cool down. It also helps the system to operate more efficiently. For quick cool down on hot days, do the following: 1. Select the vent mode. 2. Select the recirculation mode. 3. Select the coolest temperature. 4. Select the highest fan speed. Using these settings together for long periods of time may cause the air inside of your vehicle to become too dry. To prevent this from happening, after the air inside of your vehicle has cooled, turn the recirculation mode off. The air-conditioning system removes moisture from the air, so you may sometimes notice a small amount of water dripping underneath your vehicle while idling or after turning off the engine. This is normal. Defogging and Defrosting Fog on the inside of windows is a result of high humidity, or moisture, condensing on the cool window glass. This can be minimized if the climate controls system is used properly. There are two modes to clear fog or frost from your windshield. Use the defog mode to clear the windows of fog or moisture and warm the passengers. Use the defrost mode to remove fog or frost from the windshield more quickly. Use the MODE button to select the defog mode. -(Defog): This mode directs air to the windshield and the floor outlets. When you select this mode, the system turns off recirculation and runs the air-conditioning compressor unless the outside temperature is at or below freezing. The recirculation mode cannot be selected while in the defog mode. Press the defrost button to select defrost. 0(Defrost): Pressing this button directs most of the air to the windshield and the side window outlets, with some air directed to the floor outlets. In this mode, the system will automatically turns off recirculation and run the air-conditioning compressor, unless the outside temperature is at or below freezing. Recirculation cannot be selected while in the defrost mode. Do not drive the vehicle until all the windows are clear. 3-37