The AF..UP-S series actuators provide true spring return operation for reliable fail-safe application and positive close off on air tight dampers. The spring return system provides constant torque to the damper with, and without, power applied to the actuator. The AF..UP-S series provides 95° of rotation and is provided with a graduated position indicator showing 0° to 95°. The actuator maybe be stalled anywhere in its normal rotation without the need of mechanical end switches. The AF..UP-S versions are provided with two built-in auxiliary switches. These SPDT switches provide safety interfacing or signaling, for example, for fan start-up. The switching function at the fail-safe position is fixed at +10°, the other switch function is adjustable between +10° and 90°. The AF..UP-S actuator is shipped at +5° (5° from full fail-safe) to provide automatic compression against damper gaskets for tight shut off.