When the front defrost is needed, we have to crack the windows to prevent all the windows from fogging up. If the windows are up, all the windows will fog up quickly. Chevrolet told me my heater core was bad, but it is not leaking. Also, my diverter doors mainly the fresh/recirculate makes noise and will not move to fresh, could that be the cause? Thank you.
Just because there is not any anti-freeze dripping on the floor yet does not mean the heater core is not leaking. It is proabably the heater core and it has a small leak and the fluid that comes out is already a vapor.
So, you do need to have the heater core replaced.