Buick 2007 Rendezvous Owner's Manual page 209

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.
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): This mode 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.
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