I have a 2001 Blazer 4x4 and I have been smelling anti-freeze off and on with the heater on for a week or so, now today I start the truck up and put my heat selector swich in the floor position and it does not blow out at the floor, it only blows out the defrost vents, I can switch it to bi-level vent position and it blows out the vents like it is suppose too, but when I switch it to the floor. It blows back out the defrost. I hear no vacuum leaks inside the truck and check all vacuum under the hood. I see no problem under the hood, and see no vacuum leaks.

 

sounds like a heater core if it's smelling like antifreeze.

edit: god, for some reason my house smells like antifreeze now. thaanks.