Opened up my ratty heater box the other day and took a look inside. It wasn't easy. Destroyed the little silver collars that cap off the evaporator drain tubes which penetrate the firewall into the engine compartment.

Also destroyed the "h" shaped heater valve pictured below in order to remove the heater core.



At any rate, does anyone know how this heater valve works? On a 68-70 B-Body equipped with AC the heater core is rather long as though it were two heater cores joined together. Which tubes are the inlet and outlet? and what's the third tube for?