These days, you want your car’s air conditioning to work at peak efficiency—not simply to keep you comfortable and alert in hot, humid weather but also to avoid bleeding away gasoline unnecessarily. For maximum coolness, as well as maximum fuel economy, take these tips.

• Check the belt. Most AC systems run off the long serpentine belt that snakes around several pulleys next to the engine.  You can check its tension by grabbing it midway between the two farthest-spaced pulleys (with the engine off, naturally) and twisting it gently. A properly taut belt should rotate no more than 90 degrees.  Squealing or chirping, especially at startup, also might indicate the need to adjust the tension of the belt.

• Replace the cabin air filter. If your car is eight years old or younger, it probably has a cabin air filter that requires replacement every year or 15,000 miles. Check your owner’s manual. Clogged filters restrict airflow, forcing your AC to work harder.

• Crack the windows when you park. “Anything you can do ahead of time to keep the interior cooler will reduce the load on the AC system and improve your vehicle’s fuel economy,” say Paul DeGuiseppi, manager of service training at the Mobile Air Conditioning Society. Something as simple as parking in the shade or opening the windows a little (security permitting) makes a big difference. On a hot, sunny day, the temperature inside a closed car can exceed 140 degrees.

• Blow out the hot air. Opening the windows or doors when you first start up allows the hot air trapped inside to escape quickly, reducing the load on the AC system.

• Start out in “Max” or “Rec.” When you first turn on the AC, set the controls to “Maximum” or “Recirculate” and use the highest fan speed. Although this particular technique might reduce fuel economy slightly, says DeGuiseppi, it moves the greatest volume of air and also prevents hot outside air from entering, which allows your vehicle to cool down faster. Then, as soon as you’re comfortable, switch to “Normal” or “Outside” and reduce the fan speed. The lower the blower speed, the colder the air is from the system.