How many Climate Control Actuators does my car have and how to replace them?

Hello, the actuator you were at is the correct one, under the right side (pass side) dash.
In the diagram is the wire coloring to id the correct actuator. The highlighted wire (brown/white wire) is the 5-volt reference feed. The grey/blue wire is the ground, and the violet/green wire is the door position signal wire going to the HVAC module. The two wires blue/orange and brown/green wires are the two wires that feed voltage to either side of the motor depending on what direction it needs to go. I will keep updating this with information as needed. The parts list numbers goes with pic 3 and 4.

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/replace-blend-door-motor

Thank you for the information. I replaced the blend door actuator in the glove box, but it didn't fix the problem. Does it require calibration or anything else to make it work?
Are there other actuators on a 2008 Mercury Sable that control other aspects of the climate control system? Is there another one on the driver's side?

There's a blend door for each side, but if the passenger side is only blowing cold air, that's the actuator at fault. Is this a 2wd or all-wheel drive?
I don't see any reprogramming procedures, it only states to set the actuator position to the same as the failed component that came out.
There is a Technical Service Bulletin on this HVAC system. I will post that below,
I can walk you through testing the position sensor if you have a multimeter. The motor section is just the two wires that have 12-volts applied to either side. The other three wires are the position sensor.
The HVAC module is behind the center of the dashboard, so it is probably not easy to get to,
Do you hear any noise when changing the Temperature on that side? And are you able to change the air flow from the feet area up to the dash vents, okay?

https://www.2carpros.com/articles/replace-blend-door-motor

Answer to your questions: my car is a 2-wheel drive, no noise when changing temperature and there's no problem with changing the air flow from feet to vents to defrost.

I took the actuator out and re-installed it and it worked this time! I think I may have not had the wire clipped in tight the first time.

Since the passenger side actuator failed, I figure the driver's side actuator may not be far behind. For future reference, would the symptoms be just the reverse if the driver's side goes bad? (Driver's side stays cold even after adjusting the temperature.) Is that actuator exactly the same part as the passenger side, or is it different?

Glad to hear that worked for you, those are Blend doors, so they mix the incoming cold air with hot air etc. There is a in-vehicle temperature sensor in the middle of the dash, but pretty much that's it, it doesn't look like a common failure on these so I wouldn't worry too much about it until it actually fails, but yes it will be the same symptoms, you'll try to get either hot or cold out of it and it will only produce one or the other. This one is located on the driver side up under the dash, you can see in the diagram, pretty much the same procedure. It may be a different part number.

Thank you so much for you help!

you're welcome glad to help. If you have anymore concerns we're here.