Soooo... I went to the local stealership the other day and picked up (2) 19E616-A (LH/RH blend door actuators) and (1) 19E616-C (defrost actuator) for my wife's truck. I worked on the truck last night and started my efforts with the defrost actuator only because I knew for sure that one was bad and I thought it was the easiest to get to -- it was in plain sight under the dash behind the steering wheel. Once that actuator was replaced, I turned the truck on and went thru the motions with the AC to see what was still clicking so I could replace the others. Thankfully, it appears all of the clicking was caused by the defrost unit.
The defrost actuator isn't the most difficult to replace, but it certainly isn't fun. I couldn't find any videos on this particular repair, but I did read several comments from folks who have completed the repair. Some of the tips were helpful. One person said they removed the gas peddle for easier access to the actuator. I was strongly considering that to be honest. It's a very tight space up there and not much room to get tools in there with that peddle assembly in the way.
The other tip I liked was from someone that said they removed the driver's seat. Again, this is a great idea! Sadly, I'm too damn stubborn for this. I was wedged in there under the dash and pinned by the seat. I'm fortunate in some regards being tall and thin. But, it's no less difficult maneuvering in that tight of a space while looking up in a dark void.
Here are my recommendations for anyone needing to replace their defrost actuator...
1)
Remove the driver's seat. This is a no-brainer as it will make your life sooooo much easier working under the dash. It's only 4 bolts. Just do it. You don't need to completely remove the chair from the truck. Just simply slide it to the back. That will give you sooooo much more space.
2)
Remove the plastic cover (panel) below the steering wheel along with the "Steering Column Opening Cover" (part #78017A26). Removing these covers gave me a better angle to get my arm into the space so I could access the top screw. I figured this cheat code out after struggling to get my hands up into the space for 30-45 mins. Removing these panels made it soooo much easier to work in there. You'll need a 7mm and an 8mm socket or wrench to get these. I recommend a drill just to speed things up.
3)
Make sure you have as long (and slim) of a 1/4" drive ratchet as possible. This one is important as you'll need it along with an 8mm socket to get to the upper screw that is completely out of sight (no joke). I emphasize slim for the ratchet as you're working with limited amounts of space. I had to run to Lowes to pick up a new ratchet as my smallest ratchet was too short for the job and the next size up I had was a 3/8" drive with 3/8x1/4-in adapter making it too large to fit in the space.
--> Here's a link to the ratchet I picked up that worked perfectly for me...
https://www.lowes.com/pd/CRAFTSMAN-120-Teeth-1-4-in-Drive-Quick-Release-Ratchet/1000594925
4)
Have an 8mm closed-end wrench on hand as well as an 8mm ratchet-wrench to get the lower screw. You'll want both as using a closed wrench by itself will take forever. The closed wrench is to get the screw loosened enough so you can you get the ratchet-wrench in there (too tight of a space to use only the ratchet-wrench). You'll need it again to fully tighten the after replacing the part.
--> Here's a link to the ratchet-wrench I purchased at Home Depot that worked perfectly for me...
https://www.homedepot.com/p/Husky-M...2-Piece-HQRRW2PCMM/204759375#product-overview
I was able to get my hands and tools into the space and change out the part without having to remove the gas peddle. I wish I would've removed the seat as the left side of my rib cage was cramping up something serious. My right arm was pretty sore as well as I had to contort my body in weird angles to get to the part.
Hope this helps someone else attempting to resolve the much dreaded clicking sounds in their truck.