Try taking the back cover off of the freezer inside it u should have a fan see if its running if not check to see if u have got power to it if u do then just replace the motor and see if this fixes the problem if the lil coil under that fan is frozen and the fan is running then u should have a lil heat element black running through the coil see id this has power to it iif the coil is frozen and if not check continuity thru the element just take the wires off of it and see if u have continuity thru it if u do then the element is fine if u dont it needs replacing but if all this is working then ur defrost timer may be bad ull have to get the wiring diagram out usually hanging on the back of the fridge and see where the defrost timer is and see if it is working or some just have a lil sensor on the freon lines right on top of the coil to let it know when it needs to defrost that may not be working stick it on some ice and see if the element starts warming up hope this helps