In high temps, Bryant 383KAV condenser and fan will not run

Our 11-year-old attic-installed A/C unit now will not run when attic temperature is high. Thermostat clicks to engage the cooling cycle, but the blower and outside condenser do not run. A second unit in the attic for the upper floor works fine. Once the attic temperature drops at night or it isn't so hot outside, the unit works normally. When it fails, switching the thermostat fan switch to ON will not even run the fan. The thermostat is not at fault -- swapping thermostat with the working one doesn't help. Ducts are not dirty.

There is no visual damage noticed on the board. Is there a thermal sensor on the board which may be the problem? If so, is there any way to test/bypass this? Can it be replaced or does the whole board need to be changed out? Any troubleshooting ideas or manuals would be appreciated.

Thank you.

 

I'd check for a slow running drain line tripping a float switch under the evaporator coil.