I agree with keeping the R12 system. This is how the car was designed.

Since you are changing the evaporator, you should change the expansion valve too, as the two are connected. If you didnīt want to change the evaporator, then you could always flush it out. Since the system has been open for a long time, you should flush the condenser too.

As long as everything is open, change the seals as well.

R12 must use mineral oil where 134 uses PAG oil.

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