I'm puzzled - what is this switch REALLY doing?

[vidarf]

Hmm.... "Equipment cooling".. And "Exhaust"... 

[wledzian]

It selects power for the blowers that cool the flight deck instruments and EE Bay electronics.

If the switch is in 'Normal', the primary blower comes on when ground power is applied, but is otherwise off.

If the switch is in 'Alternate', the alternate blower comes on whenever the aircraft 115v bus is powered.

The plenum drawing cooling air over the electronics is fed by cabin air, with vacuum provided by the cabin air recirculating system, or simply exhausted overboard if the CARS is inactive, during flight.

[vidarf]

Wayne, check which section this thread is posted under...

[wledzian]

Ah, sorry if I spoiled the joke - I got here from the 'recent posts' list on the right side, and just happened to have that page of the system schematics open on my desk for a different issue related to other systems on the ground power bus.

[vidarf]

You didn't, my friend. I figured the "recent posts" list was the culprit.