The rear AC of my Enclave 2017 blows no cold air, in the front vents is ok. There is an actuator or something to look for? where?

ok, zero heat, but only on passenger side.
Caddy SRX
both passenger floor mode and dash vents all dead. blow but not hot.
does AC on, cold blow cold there?
front fails but not rear?
hummmmmmmmm
a complex system here, air delivery
but the SM says scan it first see if you have DTC errors?
check fuses.

me first guess is mode damper actuator failures.
and lots of tests like this in the SM

1. Place the mode switch in the PANEL position.
2. Observe the drive shaft of the mode actuator.
3. Place the defrost switch in the ON position.

Does the drive shaft of the mode actuator rotate?
etc, lots of tests in the service manual, to find dead vents or lack of heat or cold.

https://eautorepair.net/Marketing/Default.asp

Does the air temperature Blend door that the actuator moves operate ok, it moves freely?

These vehicles came with 2 types of ac controls.
The vacuum control system uses vacuum to actuate the vents and ducting from hot to cold. A lot of times the HVAC vacuum line in the engine bay (black hard plastic) is either broken or disconnected from its vacuum source.
The electronic vent control: does everything at the control knob via vent actuators and the control panel itself. With this one it could be any of the components. You would have to locate them and verify operation by moving temp/vent selector.

This model has a rear heat/cold blend door actuator. Its an electric motor that moves the duct door from hot to cold. When they wear out, they're usually stuck on the last setting

When I turn on the heat in my 2004 mazda mpv the front air vents blow heat but the rear air vents are blowing cold. I have adjusted every setting is there something I am overlooking.

If you still get cold air out of the rear vents but the front only blows hot air you may have a bad temp door actuator in the dash, it may be stuck on hot and not able to move to cold air. However if you are low on freon with a truck that has front and rear ac then there will be a temp diff between the two. If it is hot air out the front like the heat is on then you have that actuator problem but if it is cool air about the same as the outside air temp then you may be low on freon.

possible blend door actuator faulty, or a faulty blend door. This door switches from hot to cold vents. On expeditions equipped with rear AC front and rear AC have seperate actuators. Hopefully this helps!!

It is the AC vent door actuator.

Check and replace the right side temp-controller.

Hope I was avle to help, glad you up and going.