have a couple commercial A/Cs that aren't working. I don't know much about how they work but two of the units go to a large air handler. handler stays on but outside units stop around noon to 2:00 pm and one stays off while the other cycles. during the morning before it gets too hot they both seem to work fine but then as i described. the one that fails completely just recently had some kind of pressure switch replaced. before the switch was replaced it cycled quickly but now when the problem happens it does nothing. the unit that begins cycling is doing it slower than the one that had the switch replaced but as i described,, when the one with the new switch was cycling,,the other continued running fine. now the one that was running fine is cycling slower or in slower intervals and the one with the new switch does nothing. had the people that replaced the switch come check it out and couldn't find what was wrong because amazingly both seemed to work at the time he was here.