A/C question

Mine is doing the same thing. AC has been running all day and then get "dF" on the display for a few moments. Kicks off then back on and stays running. It's an Advent unit.

DF for defrost to keep the condenser from freezing up?

it would help if you gave the brand and model of your rig and the brand and model of your thermostat. It could mean "dual fuel" for heat pump and furnace operation, or it could me DF - Default factory settings.
Is the AC running correctly?

do you have a thermostat manual with trouble codes?? If not you can google one on the net.

I've heard it referred to as being "low on gas" in some cases. could also mean a condenser block (whatever that is)