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How to Replace a R12 With a R134a

Prior to the early 1990s, most automotive air-conditioning systems were cooled with R12 refrigerant. The discovery of R12 as harmful to the ozone layer resulted in it being removed from use in favor of the cheaper and more environmentally friendly R134a refrigerant. Due to the unavailability of R12, many owners of vehicles made prior to the early 1990s must replace the R12 in their current systems with R134a.

Instructions

1

Recover any remaining R12 within the air-conditioning system. Use a refrigerant recovery machine to remove the R12 and let the system hold a vacuum for at least five minutes. Repeat the recovery process if the system displays a positive pressure after five minutes. Do not release the R12 into the air, as it is a federal offense to do so.

2

Flush any remaining R12 mineral oil out of the system. The mineral oil used with R12 is not compatible with the PAG oil used with R134a. Mixing the two oils will result in premature compressor failure. Replace the accumulator or dryer with a unit that contains desiccant that is compatible with R134a.

3

Inspect the lines, expansion valve, orifice tube and pressure switches for any signs of wear. Replace the components as necessary; otherwise the components may cause the R134a to leak out.

4

Install a high pressure cut-off switch. Due to the higher pressures associated with R134a, some compressors may need such a switch for increased durability. Install the R134a high side and low side service port fittings and apply the R134a retrofit label that meets SAE requirements in an easily visible location within the engine bay, as required by Section 608 of the Clean Air Act of 1990.

5

Add the proper amount of R134a PAG lubricating oil into the air-conditioning system. The amount of PAG oil needed depends on the vehicle manufacturers requirements.

6

Evacuate the air-conditioning system with a deep vacuum pump. This will help remove moisture and excess air from the system. Allow the pump to draw at least 28 in/Hg of vacuum for 10 minutes, then disconnect the pump and allow the system to sit for another 10 minutes. If the system does not lose vacuum, reconnect the pump and finish evacuating the system for another 20 minutes.

7

With the engine running and air-conditioning system on at its highest fan setting, add the correct amount of R134a to the air-conditioning system. This amount depends on the systems capacity as specified by the vehicle manufacturer. As you add R134a, the compressor will begin to cycle on and off. Do not overcharge the system, as this can damage the compressor and other components. Use a temperature gauge to check the vent temperature inside the car. The temperature should fall at or below 42 degrees Fahrenheit.

8

Check the air-conditioning system for leaks. Some brands of R134a come with a UV leak detector that is visible under a UV lamp.