Replacing defrost thermostat in wiring harness in Frigidaire Fridge Fftr1821qwo

[FarmGurl]

I have a Frigidaire refrigerator (model # Fftr1821qwo ) that I believe has a bad thermostat. This unit has the defrost thermostat wired directly into the wiring harness. I am trying to prevent having to purchase the whole harness and plan to cut the thermostat out and wire in another one. Unfortunately I cannot locate the open and close temperature perimeters on the thermostat in order to replace with the proper replacement. I have several good thermostats lying around but from what I understand it is very important to replace the thermostat with one that has the same or very similar open and close temps. I have tried contacting parts companies as well as Frigidaire to get these specs...to no avail!!
242213501 this is the part number for the entire harness. Does anyone have any ideas or advice?

[Budget Appliance Repair]

The defrost bi-metal on this unit isn't what stops or controls the defrost - it is just a safety in-case the defrost doesn't turn off correctly to keep the freezer from getting too hot and melting the plastic liner down.

Usually on these bi-metal t-stat there will be markings on them like L47-25 meaning it turns off/opens when it reaches 47 degrees and re-closes when it cool back down to 22 degrees, (the 25 is the temperature differential 47 minus 25 = 22).

This bi-metal should probably open some where over 90 degrees.  If you check the continuity on this defrost safety bi-metal at room temp it will be closed - will only open in the case of defrost run away temp.

The thermistor which is also part of the same wiring harness is what controls when the defrost turns off or lets the board know that the coils are cold enough for defrost to come on.

The thermistor could be bad or the main control could be the problem if it isn't defrosting.

The actual specs of the defrost safety t-stat and the defrost termination temp is all listed on the tech sheet - I looked it up, here's the specs.

Safety Thermostat            Heater                Defrost Thermistor
Cut-in      Cut-out             Watts    Ohms           Termination
110°F       135°F                375         35                    47°F
(43.3°C)  (57.2°C)                                                  (8.3°C)

 

Do you actually have a defrost problem where the complete evaporator was frozen-up in frosty ice or was just the first part of the evaporator where the tiny capillary tube enters the evaporator covered in an ice ball?

[FarmGurl]

Thank you so much for the detailed reply!! The entire evaporator was frozen up in frosty ice. 

Any suggestions on how to test the thermistor...or how to find the correct one to wire into the harness.

[FarmGurl]

Hello Mr. Willie. I am still trying to repair this unit (Frigidaire refrigerator model # Fftr1821qwo). Your reply was super helpful. I didn't realize that some units worked this way (with the bi-metal not being the controlling factor for the defrost cycle). So it appears the bi-metal thermostat is working properly. However the unit is still freezing up. The entire evaporator was frozen up in frosty ice. Now I am trying to determine whether it is the thermistor or the control board that is causing the issue. Any suggestions on how to determine this or the next step I should take?

Thank you so much for you time and detailed help!!!

[Budget Appliance Repair]

You would have to get the OHM reading of the defrost thermistor and compare it to the actual temp of the tube it is clipped to and see if it matches the rating on the tech sheet.

If you don't have the tech sheets you can get them here with all the info: http://b2b.frigidaire.com/support/manuals.asp

They don't show the defrost safety bi-metal or the defrost theremistor/sensor on the parts pictures but they are listed in the parts list ref 13* as NI -Not illustrated part, (in the cabinet section).

This is the complete freezer wiring harness that contains the defrost safety bi-metal and the defrost thermistor/sensor.

Part number: 242213501

http://www.appliancepartspros.com/ShowPartImage.aspx?forumimg=242213501

Easy to replace, unplug the old one and plug the new one in and about 1/3 the price of the control board.

This is the control board which is only available as the complete control housing and control board assembly.

Part number: 5303918673

http://www.appliancepartspros.com/ShowPartImage.aspx?forumimg=5303918673