[2002Z4CSS]

Sounds like the temp blend air door is staying open to the heater core. When you move the cool and warm knob, listen for the door to close.

[gtoformula]

I got tired of hot air bleeding through the heater core during the warm months (most all of them here in Texas). I have a non AC car and it didn't have a water control valve to the heater core so hot coolant would flow through the core at all times. There is always some air bleed through the system so hot air would always come through. Stopping the coolant flow through the heater core stops the heat from coming through the heater box. I installed a vacuum water control valve a few inches ahead of the heater core nipple and used an extra vacuum fitting on the rear base of the carb to the control valve. I need to plug the vacuum fitting if I have the valve disconnected, but that is only twice a year (once when it gets warm and once when it cools down). You can also buy a mechanical control valve, but the vacuum system seemed easier as the car does not have a factory water control valve cable. Just a thought.