There are a couple of possible sources of heat in a frost free refrigerator-freezer that is operating normally. The first is the defrost heating element. It is typically rated around 300W-400W, but it should operate for only 30 minutes every six hours, or less frequently if the refrigerator and freezer doors are not opened and the seals are in good shape. This doesn't sound like it would be the source of your problem, as the heater element is mounted below the evaporator coil, which is typically located in the back wall of the freezer compartment in a side-by-side upright unit, not in the wall between the freezer and fresh food compartments. The other possible source of heat is part of the refrigerant loop, where warm, liquid refrigerant is run from the end of the condenser coil to the front of the unit, and around the doors, to heat the door frames and prevent moisture condensation there. If the temperature is excessive, you should check the condition of the condenser coil, mounted at the bottom or the back of the cabinet, as it may be loaded with dust and/or pet hair. Use a refrigerator coil cleaning brush and a narrow vacuum nozzle to remove as much dust as you can, then see if the temperature in the wall comes down. Another thing that can cause excessive condenser exit temperatures is a failed condenser fan. Units with the coils mounted on the back typically don't use a fan, but those with the coils at the bottom of the cabinet always do. Once the condenser coil is clean and experiencing adequate cooling air flow, the exit temperature of the condenser coil should be warm to the touch, not hot, and the exterior walls of the refrigerator should feel close to room temperature. The interior wall between the freezer and fresh food section should feel cold. (If you can locate the "mini manual" for your unit, it may have electrical and mechanical schematic diagrams, showing how the coolant plumbing is arranged. The mini manual may be found behind the kick plate at the front of the unit, in an envelope at the back of the unit or underneath where the compressor is, or possibly rolled up tight and stuffed in somewhere behind the plastic control panel cover in the fresh food section.)

Manufacturers recommend cleaning the condenser coils at least once a year, and perhaps every month or two if there are pets in the house.