The present invention relates to distribution of conditioned air from automotive HVAC units, in particularly, distribution systems having both front and rear components. In particular, the present invention improves the temperature characteristics of the rear floor area of distribution in the cockpit, cab or passenger compartment, in a variety of temperature modes.By providing for a valving or closing off means on a rear distribution door, regulation and adjustment of the stratification and temperature of air reaching the rear, and especially, the rear floor area of the cockpit, cab or passenger compartment, is achieved by blocking or closing off a channel between the heater core area of the HVAC and the distribution system.