There's only one way to find out so far as I know.........Pull the radio and see if you can access the switch connector
You can download free shop manuals and aftermarket diagrams on MyMopar. The 72 manual over there as well as a few others came from the efforts of the guys right here
The diagram for the AC/ heater is in the heater / AC section of the manual
Page 24-2 of the 72 Plymouth chassis manual
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