SL3 is a new standalone 10 MW data center on an existing data center campus outside Salt Lake City. Cooling systems include custom air handlers with airside economizers and direct evaporative cooling, CRAC units with and without refrigerant economizers, packaged rooftop units, custom and packaged terminal units, and a makeup water system including emergency water storage tanks, pumps, and water treatment. The main control system is a PLC based system. Our role as commissioning agent (CxA) for Phase 1 included: peer reviews at several design stages (including extensive revisions to the sequences and alarms), factory witness testing of air handlers and control systems, submittal and shop drawing review, prefunctional testing, load bank coordination, functional testing, integrated systems testing (IST), review of training and close-out documentation, and pre/post-occupancy trend reviews. We managed over 500 commissioning issues using our web-based Issues Log, hosted weekly commissioning meetings for several months (daily meetings during functional testing), and issued daily and weekly commissioning reports. After serving as CxA for Phase 1, we were elevated to Engineer-of-Record for Phase 2, which consisted of two data halls and associated electrical rooms and support spaces.