Brace yourself......
I am assuming that you have tried the "HVAC Calibration Procedure" found in the maintenance manual and on Dictator's list of remedies.... If you have not done so yet, I HIGHLY recommend trying it first.
If you are convinced you MUST replace the actuator, you first need to be sure that you have all three of the actuators in your possession. You don't want to go into this twice.....
To replace the actuators requires removal of the A/C unit from the dash. In order to get it out of the dash, you must remove the ENTIRE dash assembly out of the SSR. This is a really horrible job....... GM allocates 16 shop hours to do this. 8 hours labor to remove the dash and 8 hours labor to reinstall. You will need to begin by removing the sun visors and all of the inside windshield trim. The seats and console need to be removed and the steering column has to be dropped. You will need to disconnect the heater hoses at the firewall and the A/C lines at the firewall. Once everything (including all the in-dash wiring harness) is disconnected, the main dash assembly can be removed. This is a two man job, since the assembly weighs about 125 pounds.
There is the possibility that once you have the dash coverings off and can actually see the actuator in question, you may figure out a way to replace your one actuator without removing the whole enchilada.
Oh.... did you know that one of the actuators is no longer available????? Research required here....
I'm sorry to throw such a wet blanket onto the project, but I've been party to this before.....
Please also accept my apology for such a down post..... I'm usually much more upbeat than this.
Mike