Hey i got a 2000 s-10 blazer 4x4 4.3 with a heat problem. I seems the heat is comming out of only the defrost. I have checked vacuum lines under hood and behind dashboard and found no problem. I had glanced underneath around the transmission but saw no problem with the lines.I read there may be a switch on the tranny where 3 or 4 vacuum lines connect and can get oil in them that will cause the vacuum system to go into fault mode. That switch and the actual heat selection switch is the only things i can think of. Any got any ideas.