Over time, small amounts of refrigerant can leak out of the air conditioning system in your Dodge Ram truck. This, along with the occasional air-conditioning repair that is done, will require the system to be recharged. Recharging a completely empty system will require the system to be evacuated of any moisture. Use a vacuum pump to pull a vacuum on the system and remove the moisture. Simply topping off the system may not require this, but it is good to know how to do it anyway.
Install the A/C gauge set by locating the service ports located on the lines. Attach the blue hose of the set to the low-pressure side and the red hose of the set to the high-pressure side.