Our house/ AC system is 2 1/2 years old. We tried to fire up the AC this week to be sure it was functioning and it was fried. The tech came today and advised that the contacts on the switch unit were completely corroded from exposure to moisture from our power venter, which is located about three feet away from the condenser. My sister's AC suffered the same fate last year. We will be getting a cover for the condenser until we can get the power vent moved. The tech also told us that another common problem they see is mice making homes in the condenser units and eating the wires, as soon as one year after the initial install. Thought this might be helpful info to pass along to anyone with central AC.