Hi @josnor ,
Just verifying that it is a Frigidaire Freezer model # FFU20FC4AW2?
Only asking because looking at the parts list from two part suppliers, the condenser coils are on the outside at the back of the cabinet. (see System parts diagram). Because they are exposed to the open air there is no fan necessary to cool them down
This supplier shows the condenser coils in the System parts diagram, even numbers it, but doesn’t list it in the System parts list, although if you search for condenser in the Search by Keyword search box below the parts diagrams, left side of page, it shows that it is available as a special order
This supplier actually shows and lists the condenser coil as part #1- system parts diagram
Two things you mentioned are of concern.
First is “Only top half of my coils are frosty”. This may indicate a blockage in the evaporator unit.
Second is “I do have some oily residue around the lines”. Oily residues may indicate of leak of refrigerant. There is a special oil added in with the refrigerant in the sealed system to lubricate the compressor. If there is a leak then the refrigerant will escape undetected to the air but the oil will leave a trace.
A lack of sufficient refrigerant will cause cooling problems.
You may have to get a licenced refrigerator repairer to check the sealed system. They have the equipment necessary to check the high/low pressures in the sealed system which will indicate what and where the problem may be. I say licenced because depending on your location this is because of the environmental regulations regarding the handling of refrigerant gases. Where I am you cannot even buy refrigerant gas without a licence if you wanted to recharge a sealed system yourself.