A system and method for tissue thermotherapy including a source for generating a vapor phase media for treating a space in a human body, such as and intraluminal or intracavity space. A radially movable front plate with a ramped surface changes the radial position at which the centrifugal weight begins moving the front plate axially to compress a clamp spring and begin clutch actuation. It is isolated from this structure to prevent parallel-plate resonance modes from being set up.