CONTROL CARS AIR & TEMPERATUREHVAC heater blend door actuator is a small electric motor in your car that controls your cars temperature control system. When you turn the knob to increase or decrease the temperature or flow of air, the signals go through the blend door actuator. It also controls the defrosters and other vents. Some carmakers referred to it as an air mix door. OEM Part OE 604108, 1573517, 1574122, 15844096, 22754988, 52409974, 15-74122, 604-108 HVAC blend door actuator for impala. Replacement for Impala 2004-2014, Impala Limited 2014-2016, Corvette 2005-2013,Malibu 2004-2008, Monte Carlo 2004-2006, Buick Allure 2005-2009, Buick LaCrosse 2005-2009, Cadillac XLR 2004-2009, Pontiac Grand Prix 2004-2008. MALFUNCTION SIGNAL Knocking sound, clicking sound, or any other strange noises comes from your dashboard when you start your car or the AC system. The airflow isnt consistent, or the temperature is different, they are all the signs that your HVAC air door actuator isnt working properly. REDESIGNEDThis HVAC air door actuator features an updated outer casing to ensure it lasts longer than the other cheap blend door actuator. SPEEDTUN blend door actuator also features a more rugged internal circuit board that resists heat, corrosion, and vibration.Knocking Sound appear when you start your car or the AC system, Clicking Sound comes from the dashboard, Any Other Strange Noises, The airflow coming from your vents isnt consistent, there could be a problem with your blend door actuator. And If the temperature of air coming out of your cars vents is inconsistent, meaning it changes between hot and cold without touching the controls, that could be a sign that your blend door actuator isnt working properly. If your blend door actuator has broken completely, you might get the wrong temperature. (Knocking Knocking sounds can almost always be attributed to a failing blend door actuator. When you start your car or the AC system, the knocking sound will start.