Top of unit near fan is building up with ice, not

these units actually pretty easy to work on. first determine if the fan is or isn't working. with the door ajar, turn the thermostat up until the compressor comes on, (hopefully you don't catch it in the middle of a defrost cycle ha ha, it won't come on then. you could manually advance the timer, but save that for a "need to know" or if it matters) hold the door switch closed (pushed in) does the fan operate ?
If it doesn't, you'll likely need to replace it, outside the unlikely possibility a wire worked loose from the motor. Any service history on the unit recently ? you can visually inspect it by removing the evaporator cover/rear panel. Further to that, is the entire evaporator a block of ice ? you may have a defrost problem. I digress. you can ohm out the windings or connect a test cord to the motor to see if it runs. If the fan is working, you may have a system problem, typically you'll get a heavy frost pattern there, while little to no frost on the remaining evaporator coils if the unit is lo of refrigerant or a inefficient compressor (bad valves-not pumping sufficiently).
you can acces the fan motor by removing the rear panel inside the cabinet. BUT WAIT. you'll need a step ladder. you need to remove the top grill, first remove the screws. open the door, at the underside of the top lip around the cabinet you'll see a couple of phillips head screws, remove them. then you can take off the grill/cover. *NOTE; If you have custom wood panels on this panel it can be quite heavy, you can usually remove that by pushing the panel towards the ceiling and pulling towards you.(careful not to stretch the tension spring too much) access panel to the compressor/condensor area and unplug it from the wall. (or shut the breaker off to the unit, there are other ways, but I'll leave that to experienced techs like myself.)

rule out the motor problem and go from there. hope this helps.

good luck.