"Free" doesn't mean no equipment runs — it means the compressor, the most energy-hungry part of the system, gets to switch off while outside conditions do the heavy lifting instead.
Mechanical cooling — the refrigeration cycle inside a chiller or CRAC unit — moves heat uphill, from a cooler space to a warmer outside environment, using a compressor to do thermodynamic work against that temperature gradient. That compressor is by far the largest electrical load in a typical cooling plant. Free cooling (also called economization) exploits the fact that outside air or outside water is, for a large fraction of the year in most climates, already cold enough to absorb the data hall's heat directly or with minimal assistance — no compressor work required, or greatly reduced compressor work. The word "free" refers specifically to bypassing that compressor energy, not to the fans, pumps, and dampers that still have to run to move air or water around; those are real, metered loads, just far smaller than a compressor's.