the refrigerator half of the unit is freezing product, the freezer compartment is fine

Continental refrigerator: This is my first time with a unit like this and there is no wiring diagrams , the refrigerator thermostat is open (satisfied), the evaporator is frozen with build up.(defrost failure) not sure, how timer work or wiring path. I have a strong feeling the timer has issues. I would appreciate any advice unit, as well as defrost system and wiring diagrams, you may come up with. Also, light in top half stays on, (refrigerator compartment) Thank you