2006 ford explorer heater - blows cold air

[clevengera1954]

I am having heater problems. When I warm up the car with the heater on, cool air blows out of the vents. The temperature gauge reads about in the middle. Once I start driving the car, the heater starts blowing hot air. I replaced the heater blender door last year and it was working fine until recently. Any ideas on what could be wrong?

 

[corkey]

check the coolant level first, it could be low, and when the rpms increase it flows into the heater core , as steam, or close to it,

 

[clevengera1954]

Thanks - that was it

I checked the fluid level and it was low. I smelled the antifreeze also. I removed the overflow reservoir on top of the radiator. I found a small crack in the radiator. Looks like I am going o be replacing the radiator.