Q: How to differentiate between actuators in my HVAC system in my 2009 Chevrolet Impala

Underneath the glove box I hear a ticking sound. I only hear it when I unlock the car and open the door. After a few minutes of driving it goes away. The driver's side gets warm air (which is what it is set to) whilst the passenger's side gets cold air. Regardless of the mode of heat I'm running, outside air or central air, my passenger is forever cold. (Not sure what the actual names are bare with me) I'm fairly certain it is the blend door actuator based on the above evidence. However, I do not know which one it is. I believe my car has multiple, I think mine in particular actually has 3. I had replaced the actuator under the glove box, maybe a 2.5 years ago during the summer of 2014. I would think that actuator would last longer. My car has 124429 miles. My car has an automatic transmission.

The problem is not with replacing it, the problem lies in figuring out with actuator is acting up. It has different symptoms from the previous time.

My car has 122459 miles.
My car has an automatic transmission.