I have a 2006 Trailblazer 4.2L. First we would get heat out of the passenger side but not the driver side. Reset the actuators and heat worked perfect for about a day. Now no heat again. Trying to find the actuator(s) responsible for this issue. Any ideas here?

 

Might be under the center dashboard, they are on suburban.

 

youtube it, Im sure there are many videos on this as it is a very common failure item on this platform .