AUBURN HILLS, MI -- (Marketwire) -- 08/13/09 -- What is more fuel efficient -- driving with the windows down or using the air conditioning? The answer might surprise most people.

"It is more fuel efficient to drive with the air conditioning on than with the A/C off and the windows rolled down," said James Bertrand, president, Delphi Thermal Systems, Delphi Corp. "That's because a car uses less fuel to run an air conditioning system than it will use due to the aerodynamic drag on a vehicle when its windows are open."

The use of any automotive air conditioning system increases the load on a vehicle's engine which in turn consumes fuel. The National Renewable Energy Laboratories (NREL) estimates that traditional air conditioning systems account for approximately 5 percent of a vehicle's fuel usage each year in the U.S. and 3 percent in Europe and Japan. With a long history of developing thermal technology, Delphi continues to develop energy-efficient air conditioning systems that can cut those numbers in half. But for today's drivers, just properly using the air conditioning controls will help reduce fuel consumption.

Here are some tips to using a vehicle's air conditioning system more efficiently:

--  When entering a vehicle that has been sitting in the sun, fully open
    the windows temporarily to purge the hot air out of the vehicle. Then close
    the windows and let the air conditioning cool the passenger compartment.
--  Press the recirculation button to enable the recirculation of the
    passenger air back through the air conditioner. This button may be labeled
    as "MAX." Use of the recirculation feature will significantly reduce the
    energy used by the air conditioning system.
--  For a manual system, it is most efficient to keep the temperature
    control in the full cold position and use the blower fan setting to adjust
    the amount of cooling. The temperature control should be used to adjust the
    air only after the blower is at the lowest setting.
--  If the A/C is not as cold as it used to be, an air conditioning
    specialist can evaluate and repair the system. If there is a leak in the
    system, it should be repaired and recharged with refrigerant. It is also
    normal for the A/C system to lose small amounts of refrigerant by
    permeation through hoses over years of use. This may require a recharge of
    refrigerant.
--  A vehicle's HVAC system may have an air filter that has caught debris
    and is reducing airflow. If this is the case, the filter needs to be
    changed. On newer vehicles, this air filter could be located behind the
    glove box or below the windshield wipers. It can be changed by the
    vehicle's owner or by service personnel.