slantsixdan
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The A-body A/C system was completely redesigned for '73. Then for '74, more changes were made. The clutch cycling switch was eliminated and an EPR valve installed in the compressor (as had been done for many years in the bigger cars), but the biggest functional change was that the A/C compressor was powered in Defog mode starting in '74. This makes a huge improvement in defogger performance, and I'd like to retrofit that function in my '73 Dart. There's no physical obstacle in '73, as in '74-'76, all incoming air comes through the A/C evaporator regardless of system mode, so as long as the compressor's powered it'll condense the moisture out of the air. The question is how they made this change. I originally thought they'd just added another contact to the 6-position control switch, but that's not it; the P/N is the same for the control switch from '73 through '76. I can't find any other clues in the parts book, either. I can work around it by adding a microswitch to the control or a roller-lever switch to the heater box, actuated by the pushrod that shifts the mode door from "heat" to "defog". But before I do that, I'd sure like to know how the factory made this change. Anyone know?
