Frig defrosts but does not restart

Freezer/Frig work well when running. Defrosts but does not return to normal ops. A rapid clicking noise can be heard, like a timer. Unit must be restarted at control panel to return to normal ops. Fails to start intermittently, freezer thaws, refrigerator warms up. Replace defrost T-Stat. No joy! Ideas? ChillyDog.