Found attic air handler behind bookcase - powered on and calling for cooling but not doing anything. Checked air handler boards and thermostat IEM and found no faults - powered system completely down from outdoor unit circuit breaker - verified unit addressing correctly both inside and out - reset system power - flipped battery in outdoor temperature sensor - cycled indoor units from all thermostats - cycled attic unit several times to ensure unit properly turns off and on every time the thermostat calls for cooling. Everything appears to run normally again.