That sequencer is heat activated, it has a heater that heats up to turn the unt on and has to cool down to shut off. Is the control box getting to hot after running for hours to get it to 77 that it can't cool down enough to shut off?
Clean the evap coil!
Because the evap coil is clogged, the electrical compartment is getting very hot and heating the heat sequencer. Since sequencer relies on 24 volt W signal to heat the 24 volt coil to intiate the sequence timer it closes the circuit to the elements, but the compartment heat is heating the 24 coil instead. Now you have a runaway heat situation.
You will only see this if you put a remote temperature probe inside the contron compartment and reinstall all covers.