To reset a Unison UPSAC processor, simply reset the Sensor CEM which it resides in (usually Rack #1).
You also need to reset the Unison LinkPower Supply (ULPSA or ULPSB), which is a wall- or rack-mounted power supply. It can be identified by a Green and Amber LED on the panel, with a Reset button in between the two LED's. Make sure to fully depress the ULPSA/ULPSB reset button (use a pen or tweaker).
The ULPSA/ULPSB should be reset within 30 seconds of the CEM UPSAC.