Defrost Thermostat

After determining that it was the defrost system, I ordered the thermostat. Make sure you look closely. Mine had two thermostats, and so I had to wait a couple of days for the extra part.
1. Remove ice maker if installed.
2. Remove center casing on ceiling and back wall. There may be two screws that need removed.
3. Locate and remove two screws on upper back wall.
4. Remove back wall carefully, revealing coil system.
5. If this was the problem, the coils will be iced over and need thawed. Either time or a hair dryer...
6. The thermostats clip onto the copper tubing, simply pull them off, keeping close attention to the color of the wires.
7. Be very careful touching the bottom of the coils as the defrost conductor coils are along the bottom and encased in easily breakable glass. If you need to replace this as well, remove the center brace (wire)by pulling towards you and then down. remove wire attachments at both ends and rotate coil out of end braces.
8. Replacing thermostats...you must CUT the wires, and attach new thermostats with wire couplers or wire nuts and then wrap with electrical tape that is rated for the cold.
9. Re-attach all parts and replace back wall and coverings.
10. Enjoy!

No instructions came with new parts. Access to element was impossible until I accidentally discovered that the two styrofoam cushions at the ends of the coils were removable. Once removed, access to the heater and thermostat was very easy.

Unplug appliance, remove freezer shelf, cold air ducts, back of freezer, disconnect light, (My model does not have ice maker. This may also need to be disconnected.)
1.Remove styrofoam cushions at end of coils
2.Locate element between bottom two coils
3.Disconnect the male/female connections
4.Remove support clip under center of element
5.Remove element
6.Replace new element in reverse

Connecting the thermostat wires was challenging because they were somewhat behind the coils.

1.With styrofoam removed, unclip thermostat from coil
2.Carefully cut wires (leave enough to connect new wires)
3.Connect new thermostat wires (color of wires matched on my fridge)
4.Clip new thermostat in place
5.Replace styrofoam
6.Button it all up

With these steps, this job would take maybe 30 minutes; somewhat longer if your model has an icemaker.

Hope this helps.

In freezer box removed shelf, removed 2 screws from back panel, removed 3 plastic covers (1 with 2 screws, other 2 snaped out. Unsnaped defrost thermostat from copper tube then cut 2 wires (yellow & orange) stripped all wires back a little then used 2 wire nuts to reconnect the new thermostat and resnapped back onto the copper tube. Removed 4 screws from evaporator fan housing (original one warped from overheat and caused fan blade to get chewed up) unpluged fan motor wiring and removed ground wire and motor from warped housing, removed fan plade by just pulling on it. Installed new fan blade by pushing it on the fan motor shaft, reinstalled the fan to the housing and the housing into the freezer box. In the frig box I removed the control panel from top of the box by removing 4 screws and unpluging the main wiring plug and the defroster control then reinstalled it all in reverse order. Also had to renew the stick on foam on the evap fan housing. Over all it was an easy task.

Open the freezer panel which attached with screwws and locate the defrost thermmostate behind the back pannel. Cut off the old thermostat wires and connect the new wires.

diagram from part select matched my fridge perfect. i ordered all parts that involve defrosting coils. ( defrost heater 618, defrost thermostat 620, defrost thermostat 627 ). two wires involved with thermostat, just removed all old parts and replaced with new. Part Select videos helped demonstrate the projects well.