How to Vacuum and Refill Mercedes-Benz A/C with Refrigerant

In this article, you will find instructions on how to recharge your Mercedes Benz's air conditioning system.

Working on your Mercedes Benz's aircon system is time-consuming but not difficult; the only downside is the high price of equipment such as the AC vacuum pump and the R124a refrigerant.

If you are a DIYer with the guts and willing to trade money for knowledge, you may follow our instructions below to jumpstart your quest for practical knowledge on Mercedes Benz airconditioning systems.

What you will need




 Remove the refrigerant from the system by following the instructions below.

  1. Ensure that the vacuum pump has enough oil, open the filler cap, which is located on top of the pump; check the oil level by matching the oil level against the filler line; if the oil is low, add some oil until it reaches the line. Note: Only use an oil designed for vacuum pumps.
  2.  Attach the gauges to their respective ports. Make sure that the gauge's valves are closed before proceeding. Connect the gauges to each hose using the hose color and gauge color as reference. Connect the red hose to the car's high-pressure port, the blue to the low-pressure port, and the yellow to vacuum pump. Hold the connector with the palm and a finger on the lock to connect the manifold connector to the car's aircon ports. Press the lock, insert the connector into the port then release the lock. Note: Hoses going to the car are sized differently, and there is no risk of interchanging the hoses. 
  3.  Start the pump. 
  4.  Turn all the valves open by following the labels on the valves. This will allow refrigerant and air, and moisture to be sucked out of the system. The vacuum sound should be heard.
  5. Monitor the gauges and ensure that the blue gauge slowly turns in the reverse direction from an initial value.
  6. Once the value on the blue gauge reaches -30 psi, turn off the vacuum.
  7. Close the gauge's low and high side valves and wait for 15 to 30 minutes. If the vacuum does not hold for 15 to 30 minutes, check for vacuum leaks.
  8. Please turn on the vacuum pump and let it run for 40 more minutes and open the gauge's valves.
  9. Close the gauge's valves, then turn off the vacuum pump.
  10. Disconnect the vacuum line. Your aircon system is now ready to be recharged.
  11. Dispose of the old refrigerant properly.

 Recharge the Airconditioning System by following the instructions below 

  1. Find the sticker on the hood or near the front grill, which indicates the recommended quantity (in kgs or pounds) and type of refrigerant that your car is using.  
  2. Buy a refrigerant with the same type and quantity that is indicated on the sticker. If the quantity on the refrigerant container is less than the required quantity, buy more refrigerant containers until the sum of the contents would be equal to or greater than the required quantity. Note: When choosing refrigerants, choose refrigerants with added oil; this oil would help lubricate the aircon compressor. DO NOT choose refrigerants with leak sealers. This would do more damage to the aircon system.
  3. Remove the hose from the vacuum pump, then put some UV dye in the hose.
  4. Attach the airconditioning loading nozzle to the refrigerant by screwing it into the can.
  5. Connect the yellow hose to the other port of the nozzle.
  6. Screw down the nozzle's valve to puncture the can.
  7. Loosen the nozzle's top valve to release the contents of the refrigerant can.
  8. Purge the system's remaining air and moisture by pressing the gauges' release valve with a Phillips screwdriver for 3 seconds.
  9. Start the engine.
  10. Turn on the aircon and set the fan speed to low. This process would let the compressor turn and suck refrigerant in.
  11. Insert a thermometer to the nearest aircon vent inside the cabin. Note: the temperature reading would go up.
  12. Open the Low side (blue) valve of the gauge. Note: Place the can on a cool surface to avoid heating the refrigerant that may cause an explosion.
  13. Once the compressor kicks in, it will suck the refrigerant into the system. Notice that the low-pressure side gauge would go down while the high side gauge would slowly go up. 
  14. To ensure that the refrigerant can is empty, shake the can while looking at the watch glass situated between the two gauges.
  15. If there is no more refrigerant in the can, close the low side gauge's low side valve (blue); then close the nozzle valve and unscrew the can.
  16. Reconnect the nozzle into the refrigerant and place the can on top of a weighing scale to verify the remaining amount of refrigerant to fill up the system.
  17. Open the nozzle's valve and open the gauge's low side valve.
  18. Let the refrigerant go into the system until the calculated remaining weight is consumed. For detailed computation, see How to load the exact amount of refrigerant in the system on the Frequently Asked Questions section.
  19. Shut off the Gauge's valves.
  20. Shut off the manifold gauges, then disconnect the hoses from the car.
  21. Screw the caps on the a/c lines. Do not tighten them too hard. 
  22. Check the temperature reading from the cabin; it should be 42 to 43 degrees Fahrenheit.

Important: Always wear eye protection and gloves all the time when working with refrigerants. This would ensure your safety when accidental exposure occurs. 

Frequently Asked Questions

How long does recharging AC last?

  •  Your air conditioning is not something that runs constantly, so unless your A/C system has a leak, you can usually expect a recharge to last at least three years or longer.
How to Vacuum and Refill Mercedes-Benz A/C with Refrigerant Working on your Mercedes Benz's aircon system is time-consuming but not difficult; the only downside is the high price of equipment such as the AC vacuum pump and the R124a refrigerant.