A two-phase thermosyphon cooler coupled with phase change material (PCM) energy storage was built to demonstrate a concept for cooling a 26 kW actuator motor. FC75®, a Fluorinert® compound, was used as the working fluid to transfer heat to the phase change material, acetamide. The PCM was contained in alternating layers of a plate-fin compact heat exchanger core. At the 90 percent power condition the peak motor temperature was within 90°C of the heat sink, showing good source to sink thermal coupling by the thermosyphon and conductive links. Conversely, when the motor was cooled by natural convection and conduction alone, the peak temperature was 190°C above sink temperature. Testing shows that the PCM material provides additional useful thermal inertia during the melting process. However, test data revealed that the melt temperature of the acetamide had been depressed from 80°C to 68°C by absorbed water, highlighting the need to process the PCM in a dry atmosphere. The lower melt temperature did not affect the overall thermal test results, and the PCM heat of fusion was not affected by the water.