My 96 S10 Blazer defroster has a problem. The switch is set to defrost, the fan is working fine, but only when the temp is set to cool. When I set the temp to anything warmer than halfway, most of the air stops blowing through, even though the fan is still working. Please help.

 

Look for threads on the engine compartment vacuum hoses that deteriorate and leak. Then another common failure is the blend-door actuator failing.