Your drain tube may be stopped up with ice at the upper end because it drains too slow because it's stopped up at the lower end in the evaporator pan under the unit at the floor. It can get dust and mold in it. Once you get the ice out at the top a little air pressure will usually clear it out. Flushing it out with hot water and clorox may help. Make sure it drains quick enough. The drain should be located below the evaporator coils in the lower back of the freezer.

It looks like you have a machine compartment on the back cover you may be able to access the condenser coils thru it.
You may can access it from the front at the bottom by removing the kick panel.

Cleaning the coils may help the run time. Is the temp OK in the freezer and fridge.