I have a robertshaw digital non-programable hvac thermostat, no batteries. The overflow condensation switch tripped the unit off. we fixed this but now my thermostat goes blank when I switch it to the AC. The unit continues to run and I must manually turn it off. What could be my problem. All worked fine until the unit was cut off by the sensor.

That float switch interrupts power to the thermostat to stop making water(cooling the house).
I would try to turn off the Breaker to the Air Handler and back on, hopefully it will reset.
Many Digital need batteries?
I take it you corrected the clog.