My blower for heat/ac works but its not putting out any heat!

Hello, Get the engine warm, and then see if the heater hoses are both getting hot. The other thing is that the mode door which blocks the heater core could be stuck, broken, or could have a bad actuator. I see that you said they were checked, but does the sound of the airflow change like normal when you switch from cool to heat? Do you hear the door move and stop when the switch is changed back and forth?

Also,make sure the coolant level is full or you'll get no heat if it's low..some reports of low coolant with no sign of a leak..also a NOTE>> Flush cooling system every 60,000 miles on Hummer H3 GM recommends replacing the engine coolant at 100,000 miles; however, our technicians tell us that the coolant may become contaminated and require a complete cooling system flush every 60,000 to 70,000 miles.