Over the winter I installed a digital Thermostat on my 10+ year old Heil Central Air system, and everything has worked great for a few months. Last week the system shutdown while the AC was running and never came back on. I turned the power off to the system at the furnace and outside I used a garden hose to clean off a small build up of cotton seeds on the units cooling fins. I restored power to the system and set the thermostat to On and Cool, and ever thing worked great for a few more days. Then the system shutdown again and I was unable to get it to run using the same steps above. After a few days of no AC I was going to call a repairmen after I got home from work. To my surprise when I got home the house was nice and cool, and the system running great. It had rained a few hours that day, but I'm not sure that was the fix because the next day was dry and hot and the system continued to run great. The following night it shutdown again, and has yet to restart. If anyone has any ideas please respond.

The system is still in a cycle of everything running great for a day or so then shuts down for a day or so. Could this be some type of sensor?

Is there some sort of shutdown time on that digital stat, like a vacation setting or something? Did this occur before you installed this stat?