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I've converted mine over and R134A works just fine. Maybe the air is a couple of degrees warmer than if I was running R12 but certainly within acceptable ranges. On 90+ degree days the air will blow out of the center vent at about 50F.

The POA valve is located on the outlet line of the evaporator and it maintains a specific pressure within the evaporator (35 PSI I think). It has a sensing line that runs down into the evaporator core that senses the pressure inside the core and limits the amount of refrigerant that can get back to the compressor.

The expansion valve meters the refrigerant into the evaporator. It drops the pressure of the liquid in the line from the dryer and causes the refrigerant to flash to a gas.

You don't have to replace either the expansion valve or POA valve unless they are defective. But the R134A works at a slightly different pressure than R12 which results in a less efficient system when you use an R12 POA valve. I suspect that if Year One sells a retrofit POA valve then they have recalibrated on to work with R134. It probably isn't visually correct. You do have to replace the dehydrator (dryer) with one used with R134A. You also need to flush out and replace the compressor oils, as the type of oil used in an R134 system is not compatible with the oil from an R12 system. Other than that you should also replace all of your O rings with the newer high temperature green O rings.

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Mark Canning
1969 Indy Pace Car
350/300HP RPO Z11
My 69 L48 - 350/300HP Engine
 
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