Issues with your air conditioning in your 3rd Gen Ram 2500/3500 can stem from a few different areas. One of the most common failure points is the heat & a/c actuator. This actuator controls the temperature of your air conditioning system. A faulty actuator will not allow the temperature door to move causing your a/c to be stuck at one temperature. This is a direct Mopar replacement part and installs using the factory hardware. If you are wanting to replace all the actuators in your single zone Ram, you will need 4 of these actuators to rebuild the complete box. If you have a dual zone, you will need the 4 actuators the same as a single-zone. However, you also need one additional actuator (five total) to complete the box. The additional actuator part number is (MOP-05073983AA). The Mega Cab is single zone or dual zone. There are no additional actuators. A linkage rod makes the rear vent door actuate.