Running the AC units with the drain valves closed may have damaged the units. It is unfortunate about the valve mix up but the AC drains normally are small hoses while the holding tanks have large hoses so it should have suggested these were not the right valves.

The other issue with AC in the climate is that frequently people run the AC while having the cockpit door open for much of the time. This allows too much humid air in while the heat exchanger is hard at work. The result will be ice build up on the exchanger resulting in limited air flow and poor cooling. This can be corrected by leaving the units off for a number of hours or if they have a heat setting it can be run for 20 minutes or so to melt the ice.