2009 Dodge Ram 1500 Pickup Owner Manual - Page 304

302 UNDERSTANDING YOUR INSTRUMENT PANEL Recirculation Control When outside air contains smoke, odors, or high humidity, or if rapid cooling is desired, you may wish to recirculate interior air by pressing the RECIRCULATION control button. Recirculation mode should only be used temporarily. The recirculation LED will illuminate on the blower control knob when this button is selected. Push the button a second time to turn off the Recirculation mode LED and allow outside air into the vehicle. NOTE: In cold weather, use of Recirculation mode may lead to excessive window fogging. The Recirculation mode is not allowed in the Floor, Mix and Defrost modes to improve window clearing operation. Recirculation will be disabled automatically if these modes are selected. Summer Operation The engine cooling system in air conditioned vehicles must be protected with a high-quality antifreeze coolant to provide proper corrosion protection and to protect against engine overheating. A solution of 50% ethylene glycol antifreeze coolant and 50% water is recommended. Refer to "Maintenance Procedures" in Section 7 of this manual for proper coolant selection. Winter Operation To ensure the best possible heater and defroster performance, make sure the engine cooling system is functioning properly and the proper amount, type, and concentration of coolant is used. Refer to "Maintenance Procedures" in section 7 of this manual for proper coolant selection. Use of the air Recirculation mode during Winter months is not recommended because it may cause window fogging.