My a/c will not blow out the front registers...it only blows out the defrost vent...I replaced the a/c/ heater control with no change...could there be a servo giving me that problem. Any help please...thanks.

 

most chevy products now use electronic actuators to move the temp, mode and recirc blend doors. you may have a faulty actuator if the mode door does not move out of the defrost position.

if you can find the actuator (I'm not sure where it is for a trailblazer), see if its rotating when the mode control **** is adjusted.

A body code may be set in the HVAC or BCM but you would need a full function scan tool to retrieve it. With a scan tool you could also verify movement of the mode door by watching the "door position counts" change as the door moves.