how does theAWD work on a 2006 mercury mountaineer v6 luxury model, can find no switch on dash.?

All Wheel Drive (AWD) Transfer Case Torque from the transmission is transferred to the input shaft through the planetary gear assembly and out the rear output shaft. Torque also flows through the planetary gear assembly to the drive gear outward to the driven gear. The torque flow continues from the upper drive sprocket through the drive chain to the lower drive sprocket to the front output shaft. The open differential provides 60% of available torque to the rear and 40% to the front, between the rear output shaft drive gear and the front output shaft driven gear.

sounds like yours is AWD all the time no switch.

No, there is a 4WD control module that engages the 4WD.

Yours isnt AWD all the time then you have this style.1-Speed Torque-On-Demand Transfer Case The transfer case transfers power from the transmission to the rear axle and front axle when the electromechanical clutch is activated. The electromechanical clutch assembly drives the drive sprocket after the 4WD control module activates the clutch coil. The drive sprocket turns the drive chain that rotates the front output shaft and the front driveshaft. Still no switch on the dash it does it on its own.

I have a 2006 Mercury Mountaineer Premier 4.6L V8 AWD. You can lock the AWD drive in the ON position via the dash computer. Press the SETUP button once and the screen will say PRESS RESET TO BEGIN SYSTEM CHECK press SETUP again and it will say AWD: AUTO or LOCK press the RESET button to move the selector from AUTO to LOCK. A dash light will come on that says 4X4.