HVAC Guru's: Question about ventilation circuit

[410440]

My question is this:

I have the VENTILATION switch on my main floor below my thermostat, which turns on the furnace blower and upstairs bathroom fan to exchange the air in the house, I understand how this works...

But in the basement as you can see in the pictures, I have another switch thats labeled VENT ON / OFF, When the upstairs ventilation switch is turned on and running, if i go down stairs and turn that VENT switch to ON, everything shuts off.

If I leave the upstairs ventilation switch OFF and go turn on the VENT switch in the basement, nothing happens.

I cant quite figure out what the basement switch does or why its needed - you can see my pictures below.

I am assuming the 14/2 household wire that runs into the basement VENT switch is directly connected to the VENTILATION switch on the main level, but it runs into my cold air return so i cant be 100% sure thats where it goes...

Any ideas ?

[mobius]

My guess is that whoever installed the switch put the cover on upside down. If you take the cover off and look at the switch: With the brass colored terminals on the right side, the on position will be at the top.

Edit: Also, what a shitty wiring job.