I am re-connecting the Heater Controls using a new Vacuum controlled Valve on the Manifold and new Vacuum Lines.There's lots of Vacuum going into the Temperature Control Valve (Cricket Valve) in the Heater Box  but very little coming out to go to the Valve on the Manifold. Blowing compressed Air in both Directions does not go through the Valve even in high Heat Position which should allow Air through.  Whats inside the Cricket Valve that would cause little Vacuum out? Is it not just a Mechanical Valve or is there more to it?