If you can keep gear dry and cool with ambient air temps, then forget A/C.
If there is moisture or humidity but still reasonable ambient temps then look at water cooling. I live in Queensland, Aus. and we see loads of humidity that is usually sea air laiden with salt. The last stuff you don't want around gear. I have solutions with some customers where the servers are modded with water cooling gear (CPU's, GPU's, DIMM's) then run external facing quick-disconnects. The rack then has a pair of header lines wich the servers are connected to and then also a large radiator in the top of the Rack cabinet. This is to collect any other heat in the cabinet from things like PSU's and HDD's. The coolant in the system is kept as a local closed loop with a heat exchanger (stainless steel) that then exchanges heat from the closed loop to water from a swimming pool.
Simple temp sensors or temp switches keep an eye on the servers, if the coolant stops, servers shut down.
It does sound complicated but when done, is actually pretty straight forward and can be done on a budget. When this is compared to hardware and install costs of A/C and then the running costs, saving come quick.
There is also immersion cooling for the keen.
