A/C & Non A/C heater fan switch

[VFilms]

I'm restoring the Heater-A/C system on my '66 Belvedere. And aside from the 'is there a controller that replaces the # 2587564' question, I have a fan switch question.
I have a non A/C fan switch and my original A/C fan switch. The non A/C switch has 4 positions while the A/C switch has 3. What is the reason for this? I plan to use what came with the car, but just wonder about the difference. Also, if anyone needs the 4 position non A/c switch, let me know and it's yours.

 

[RussT Plymouths]

3 position AC switch uses the "Off" on the push buttons, killing power to the switch.
4 position Non-AC switch has "Off" full down.

 

[VFilms]

3 position AC switch uses the "Off" on the push buttons, killing power to the switch.
4 position Non-AC switch has "Off" full down.

Thanks very much. Greatly appreciated! This is why I love this forum. Always someone knowledgeable and willing to help.