A vehicle heating, ventilation, and air conditioning system includes front and rear HVAC systems. A controller receives data from front and rear control panels and controls the front and rear HVAC systems. Actuating a rear manual button on the front control panel allows control of the rear HVAC system via the rear control. Engine coolant temperature is used to judge if the vehicle has been inoperative for a long time. If the vehicle has not been inoperative for long, and the rear manual button was actuated prior to the vehicle shut down, rear manual control over the rear HVAC system is enabled. If the vehicle has been inoperative for a long time, or if the rear manual button was not actuated immediately prior to vehicle shut down, rear manual control is not enabled, thereby preventing operation of the rear HVAC system by the rear control panel.