Wait a second. Maybe that's the problem we're having, and the reason they can't reproduce the problem by shutting off the power to the AC unit itself. Can you describe in more detail exactly what the problem was?

Well, our A/C unit is a standard water cooled one, with redundant compressors but a single water supply, alas.

The long answer, as I understand it: the fan blows server room air over coils (think radiator) filled with coolant (they used to use freon, I have no idea what they use now). The compressors pull the heat from the air by vaporizing the coolant. The coolant runs through cooler water, recondensing the coolant for another cycle, and handing the heat off to the water. The now warmer water circulates from our server room to the cooling tower on the roof, with radiators that push the heat into the air, and returning cooler water for another cycle.

When they stop the water circulation, the water sits and gets hot, the coolant can't recondense, and the overload circuits shut the compressors down to keep them from blowing up (or at least leaking all the coolant under extreme pressure).

FWIW, I can almost never get the building to admit to this being the problem, but our A/C unit reports the error so we know that's what happened. We have one building engineer that'll tell us that, yes, their night guy shut it down for half an hour, by mistake... "Sorry."

They're supposed to notify us before any scheduled maintenance on the water system, and any time they have an emergency shutdown. So far, they've never actually notified us, so we got our own monitor. <sigh>

Edit: And we're looking into a secondary A/C unit that is air based, and push the heat into an adjacent storage room on the building's main A/C, but that'll be several thousand bucks, and we move, um, glacially on that sort of purchase.

-jk