How To Convert Mercedes Benz 300D Air Conditioning System

You can learn how to convert Mercedes Benz 300D air conditioning system from R12 to R134 if it stops working. All vehicles built before 1995 had R12 Freon in the AC. It is becoming more difficult and expensive to obtain R12 Freon while you can purchase R134 coolant anywhere that sells automotive parts. With the right tools it is possible to convert the air conditioning system in your 300D Mercedes to an R134 system following these steps.

To convert Mercedes Benz 300D air condition systems, you will need:

  • Refrigerant recovery machine
  • R134 retrofit kit
  • Manifold gauges
  • Vacuum pump
  • R134 Freon
  • Mercedes Benz 300D service manual
  1. Remove the old R12 Freon from the air conditioning system by connecting a refrigerant recovery machine to the low-side air conditioning service port. Note that it is illegal to recover R12 Freon from your vehicle without a special EPA certification. You must take your vehicle to a licensed mechanic to have the R12 Freon properly removed from the air conditioning system using a refrigerant recovery machine, if you are not EPA certified to perform this maintenance. 
  2. Open the engine compartment and locate the high and low pressure couplings on the air conditioning system. Install retrofit fittings onto the old high and low pressure couplings by screwing on the new fittings over the old fittings. These will allow your vehicle to connect to air conditioning repair tools.
  3. Hang your manifold gauges on the hood latch and connect the high and low side tubes to the respective ports on the Mercedes 300D. Hook an air conditioning vacuum pump to the neutral port and draw a vacuum in the system for approximately one to two hours.
  4. Disconnect the vacuum pump. Start the vehicle and turn on the air conditioning compressor. Note that the compressor may not actuate; some vehicles have a low pressure cut out switch.
  5. Check the specifications for the Mercedes Benz 300D air conditioning system to learn how much coolant to add. Connect a can of R134 Freon to the neutral hose on the manifold gauges. Open the low side port on the gauges. Note that you should never open the high side port as it is extremely pressurized.
  6. Verify that the air blowing out of the vents is cold. If not, check for leaks in your air conditioning compressor.
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