How to Charge the AC in a Mercedes Benz

1. Visit an auto parts store and purchase a Refrigerant Kit consisting of a canister of 134a refrigerant, a pressure gauge and a connection hose with a coupler.
2. Turn on the vehicle's engine and set the air conditioning system to maximum cool. Open the hood of your vehicle and locate the low-pressure service port on the larger-diameter aluminum tubing next to the engine on the driver's side.
3. Remove the protective cap from the low pressure service port, attach the Refrigerant Kit hose and gauge to the service port using the coupler at the end of the hose, and read the pressure in your air conditioning system. A low-pressure gauge reading is in the green range, and a normal reading is in the blue range. Pressure readings in the yellow and red ranges are too high.
4. Charge the air conditioning system if the refrigerant level is low. Shake the refrigerant canister well, securely tighten the charging hose to the refrigerant canister, and connect the charging hose to the low-pressure service port. Press down the button on top of the refrigerant canister to begin charging. The canister should should be held upright and shaken or agitated every two or three seconds.
5. Stop recharging the system once the pressure gauge readings reach the normal range (blue). Detach the connection hose from the low-pressure service port, replace the cap, and close the hood.