Okay, I have a 1998 GMC Sonoma with a V-6 Vortec. i recently discovered that no heat was comming throught the vents when on, just air. trying to find any suggestions on what to check. The engine uses GM DEX cool. i have replaced thermostat, truck is not overheating. no leaks from anywhere, no puddles from the heater core. blower works just no heat. could it be the core is just blocked? i have checked fuses as well, they are fine. Please Help!!!!
MRC

 

Flushed system and heater core, replaced fan clutch, now i have all the heat i could want