Found this info in one of the Frigidaire dryer service manuals.
Display shows: F 05
Indicates: A problem with the key pad.
Correction: Disconnect the keypad ribbon from the
control and reconnect the ribbon. Try
all keypad switches to see they all function
correctly. If they do not, try cleaning
the end of the ribbon with a soft cotton
cloth. Reinstall the ribbon and program
the dryer to operate. If the code,
reoccurs replace the touch pad.