Tom, you hit the nail on the head. The R-12 systems were able to use a comparatively smaller condenser (R-12 is a more efficient refrigerant) than the R-134A systems. Unfortunately, I don't know how to order an oversized condenser for classic cars, so your A/C performance suffers (especially at slow or stopped speeds.) Once you get the car moving, there is better airflow permitting better A/C performance. To some small degree, a pair of electric "pusher" fans in front of the Condenser will aid in heat exchange at slow speeds, and may to a lesser amount aid in radiator airflow as well. Still, this is a band-aid on an artery.
Your other 2 cars, and the aftermarket A/C setup are all designed with R-134A in mind. Thus, they perform MUCH better than a R-12 system that has merely had R-134A refrigerant installed.
The analogy I use is: Early HP muscle cars forced to detune on today's fuels. Not as efficient as a car designed from the beginning with lower octane fuels in mind.
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Much love out to my Peeps
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"I work in high speed aluminum tubing."
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