How to Change R12 to R134

by Dustin Thornton

Over time, vehicle air conditioning systems tend to loose their Freon charge and stop blowing cold air. Recharging your air conditioning system can be as simple as heading to the local auto parts store and picking up a few cans of R134 air conditioning refrigerant (unless your car is a pre-1995 model, when cars contained R12 Freon.) Since R12 refrigerant is many times more expensive than R134, it is harder to attain and requires a special license to purchase. It is often easier to change your R12 system to an R134 system than to recharge an R12 system.

Dispose of any R12 Freon that is still in your air conditioning system by allowing a certified professional to remove it via an R12 recovery machine. Note that it is against the law to release R12 directly into the atmosphere and you must have a special license to handle R12 Freon.

Locate the high side R12 service port, which is between the air condenser and compressor. Place the retrofit R134 service port fitting over the old R12 port and screw it on until it is hand tight. Tighten the R134 retrofit service port fitting to 20 foot pounds of torque using a torque wrench. Repeat this process on the low side R12 service port.

Hang your manifold gauges on the hood of the vehicle, so that you can see them, and ensure that the valves are both closed. Connect the blue hose to the low side service port and the red hose to the high side service port. Connect a vacuum pump to the yellow hose, open the center valve and low side valve and draw a vacuum into the system for 60 minutes or more.

Close the low side valve and the center valve on the manifold gauge and disconnect the vacuum pump. Add R134 air conditioning lubricant to the system by connecting a can of R134 oil to the manifold gauge and allowing the vacuum draw in the oil. Refer to your service manual for the exact amount that you should add. Do not do this if the Freon that you are going to add already contains oil. Close all the valves on the manifold gauges and disconnect them from the air conditioning system.

Refer to your service manual for the exact amount of R12 Freon that your vehicle requires. Note that you will only be adding 90 percent of that amount, since you need less R134 than R12. Overfilling can damage the seals on your air conditioning system, causing it to leak.

Connect the first can of Freon to the T-valve, ensuring that the valve is not open before you do this. Start your engine and turn the air conditioning up to maximum, as well as turning the fans to high. Connect the T-valve to your low pressure side and open the T-valve allowing Freon to enter the air conditioning system.

Place a thermometer next to the air conditioning vents in your vehicle. Monitor the inside temperature of the air conditioning periodically while you are adding Freon, to ensure that you do not have a Freon leak. Continue adding cans of R134 Freon until you have added 90 percent of the maximum capacity.


  • close Never let R12 Freon freely escape from your air conditioning system. It can damage the environment and it is illegal. You must be a licensed professional to handle R12.

Items you will need

About the Author

Dustin Thornton has been writing since 2003. He has served as a newspaper columnist for the "Troy Tropolitan" and a contributor to various websites. Thornton received a partial scholarship for an outstanding essay in 2003. He has a Bachelor of Science in business administration from Troy University.

More Articles

Photo Credits

  • photo_camera moteur image by berdoulat jerome from