How to Mix R134A with R12

R-12 freon and R-134 freon cannot be mixed or used in the same system, but an existing R-12 system can be converted to an R-134 system. Convert your vehicle's air conditioning to R-134 to save money; R-12 is extremely expensive and can only be recovered and recharged by a certified professional. No vehicle produced in the United States has used an R-12 system since production of the freon was stopped in 1995.

Convert your R-12 system to an R-134 system with a retrofit kit.

Any R-12 remaining in your car must be recovered by a certified professional using a specialized recovery machine that prevents leaks into the atmosphere. It is illegal to handle R-12 freon without a license.
A retrofit R-134 service port must usually be installed before the system can be recharged with R-134 freon. To do this, simply place the new service ports over the existing R-12 ports and tighten to 20 foot-pounds of torque.
Attach the recharge service hose on your car's air conditioning system to the low pressure gauge. With the can held vertically, open the valve to release the air from the hose. Close the valve and the hose will fill with freon.

Turn your car on and turn the air conditioner to maximum power. Fasten the freon-filled hose to the air conditioner's service fitting and open the valve. Fill the system to 40 psi and close the valve.