A method of controlling the temperature of an ultrasonic blade between two temperature set points includes applying a first power level to an ultrasonic transducer to set an ultrasonic blade temperature to a first target temperature T1, monitoring a phase angle ϕ between voltage Vg(t) and current Ig(t) signals applied to the transducer, inferring the temperature of the blade based on the phase angle ϕ, determining that a transection process is complete, and applying a second power level to the transducer to set the blade temperature to a second target temperature T2. The transducer may be coupled to the blade via an ultrasonic waveguide. The first target temperature may be optimized for vessel sealing and the second target temperature may be optimized for clamp arm pad life. The control circuit may determine that transection is complete by determining that the ultrasonic blade contacts the clamp arm pad.
