There seems to be two actuators that fail most commonly. The one in my posts below is for the knob that controls the vents like defrost to dash to floor ect. The other one that fails is for the temperature control knob. This happens when you move the control nob from hot to cold or vice versa and requires the dash to be removed to access for repair. In my case this caused the heater to not work. When I would go from cold to hot I could hear the little lever on the actuator inside the dash pop off the track and the vents would remain cold even with the knob turned all the way to hot. There is a solution to this. You start with the knob on cold turn it very slow like one tiny click at a time until you hear it pop off the track then you back it up a few ticks very slowly until you hear it pop back in the track then you can turn it all the way and it should "catch" and bring your heat on. It takes a little messing with but I can now get my heat to come on in the first try. It is annoying but better than no heat and the alternative will be tearing into the dash.
A lot of people complain about the clicking actuator when going from defrost back to normal. You can fix it yourself if you have some patience. The updated part number is 27743-ZS00A. It is like 40-50$ from the Nissan dealership.
old one on left:
I believe there is a plate above the gas pedal (mine wasn't there) so remove that to start and lay on your back and look up above the gas pedal and you should see the actuator as pictured below. I propped my feet up on a chair.
Pull the power connector from the top of the actuator. There are three screws that hold the actuator to the mounting plate. Two on the bottom that you can see and one that is up top that you have to get by feel. They should be 5.5 mm unless like me yours had been replaced before.
Once the screws are free you can pull the actuator out and you'll likely have the white cam plate come with it. I did, so I pulled off the mounting plate that the actuator had been bolted to then re-aligned the cam gear as pictured below then put the mounting plate back on.
Now here is the tricky part. Maybe someone will have a better way for this but if you are like me I went into it not knowing and this was how I figured it out. Get the new actuator and plug it in, don't bolt yet. You'll notice it has a little gear with specific grooves to fit into the grooves on the hole in the cam plate. I plugged the actuator in and turned the vent knob until the gears moved and lined up with how I had the cam plate set then I was able to slide the new actuator into place and put the screws back in and was then good to go. You could probably just move the cam plate to line up the gears but it kept falling off for me.
So now I am clicking free and hopefully this helps save someone some time.