mtnflyer
on the bleeds.-one bleed needed for air conditioning.the VCM is not unlike those wall unit airconditioners found in hotel rooms.it needs room air to work-takes it in the bottom and forced to cool and exhausted out the top.so to get any air into the cabin we need air(envir) thru the bleed valves and this air is then give to the a/c unit the VCM to get cooled further,if needed.
I have to disagree with you here. The VCM will function all day long without any bleed air. The blowers simply recirculate cabin air past the VCM-cooled heat exchangers. Additionally, the ACM air (from the bleeds) is completely separate and running through a different circuit than VCM/Blower air. From the FlightSafety B19000 manual, page 9-5:
"Two evaporator blowers recirculate cooled cabin air. Evaporater coils are mounted on the inlet side of the evaporator blowers to facilitate the exchange of heat between cabin air and the cooling freon when the vapor cycle sytem is operating. The evaporator blowers recirculate cabin air through the eyeball outlets".