[rohrmann]

We had an issue several years ago, and thought it was the thermostat. It turned out to be the box under the A/C. There had been enough moisture that got inside the box and corroded the circuit board and the cable connectors. Not sure how the moisture got inside, but the damage was done. I ordered a new box, and replaced the bad one and all was fixed. The special "phone" cable goes from the thermostat to, on ours, the main A/C which is Zone 1. That is where the furnace control cables connect to the system. Then, on rigs that have a second A/C, there is another one of those phone cables that goes to the second A/C, which would be Zone 2. The photo shows the corrosion on the circuit board and connectors.