My name is Peter. I am a retired field service refrigeration technician.
How do you know you fully defrosted the freezer? You have a defrost timer and heater to do that. Unplugging your unit for a few hours may not be enough.
You need to remove the lower back wall cover. There are several screws holding it on and the rubber molding around it easily pulls out.
Up plug your unit and remove the lower back cover.
1.) Frozen Drain - Your unit goes through a defrost cycle every 8-10 hours. During the time your freezer shuts down for 20-30 minutes except for your light. If you have a frozen drain, the condensate builds up behind the lower back wall until the cooling(evaporator) coils become plugged up and you do not get any air flow. You may even have a solid block of ice.
Repair: Using a hair dryer (DO NOT Use Metal Objects. You may damage the coils.) slowly defrost the coils. This will take 2-3 hours.
2.) Cooling (Evaporator) Fan Failure - Assume the coils are not iced up. Is your evaporator fan running?
Part #: 3-60336-001 Cost: $115.00
Check it out: With a multi-meter set to the lowest Ohms (Omega Symbol). Is the motor humming, Then it is bad and needs to get replaced.
Unplug the unit. Disconnect the motor. Put one meter lead in one connector socket and the other lead in the other motor sock. You should get a reading of "0" Ohms if the motor is good. Anything else the motor is bad and need to be replaced.
3.) Defrost Timer - Pull your unit out to access the lower back. With your unit plugged in, take a small flat head screw driver, insert it into the slot on the time. Turning clockwise one turn at a time, until the freezer shuts off. If you have turned one full cycle, then you have a bad timer.
Ok. The unit shut down except for the light. Observe the metal bar below your cooling coil. Is it hot? If not then you may have a bad defrost heater. Lets check it out - Unplug your unit. Once again with your multi-meter set on the lowest Ohms, disconnect each ends of the wire connectors. Be careful not to touch the fins on the cooling coil. They are razor sharp. The connector are hard to pull apart. Put one meter lead in one connector and the other meter lead into the other connector. If you do not get a Ohm reading between 50-250, then you have a bad defrost heater.
Substitution: 3-80405-003 Cost: $56.00
This is a glass tube with a spring in it. If it is burner or the spring is broken then you have a bad defrost heater.
4.) Refrigerant Leak or Obstruction - With the unit plugged in. Lay the lover cover the cooling coils. Close the door and wait 30 minutes. Remove the cover. Do all of the coils have a nice frost pattern? Is there a block of ice in the upper right hand corner of the cooling coil. If so you either have a refrigerant leak or an obstruction. In this case the repair will cost you $450.00-$500.00.
5.) If all of the above is good, then you may have a Bi-mel problem. In the upper right hand corner of your cooling coil there is a thermostat. This controls the temperature and compressor start-up. This may explode in the back. Check to see if it is intacted.
5.) Bad thermostat - These can not be checked for failure. If you have check all of the above this may be your problem.
Substitution: 4-83053-003 Cost: $68.00