I also posed this question on the ratsun Facebook page and someone said:
210/B310 Factory AC did not have a separate AC switch. To turn on the AC, you move the top lever all the way to the left and a microswitch inside on the lever closes, and kicks on the compressor.
This makes some sense since my parts book has the same number for the heater control as the air conditioning control unit. I also just got my hands on an install manual for air conditioning. Now that I know about this microswitch it makes more sense what I'm seeing in the service manual.
Maybe there is supposed to be a light some place but maybe just for indication that it switched over? I'd be interested to know if that's the case.
Here's the drawing of the microswitch