Making a Replacement Part for the Unavailable Three-Wire Defrost Thermostat 63001599, KS-2N-MF, AP4072639. Replacing the Unavailable Defrost Heater AP4072093 or 63001595.

1/18/2017:  The defrost thermostat went bad on my 10 year old Admiral 21 Cubic Foot refrigerator model LTF2112ARW.  I knew that because there was no continuity between the white and orange wires when the thermostat was submerged in a cup of ice water.   There was also heavy icing and frost on the back wall of the overhead freezer compartment, and the refrigerator below was not cooling.  When I looked for the necessary replacement part on the web, 63001599, every place I went said that the part was no longer available.

Hoping to keep the fridge alive, I saw that the broken thermostat was labeled KS-2N-MF, with a rating of 16.2/-5.4.  When I Googled the part number, I found it was made by a Korean company, and all the specifications for the part, including a schematic were found here:   http://www.pnacorp.com/mobile/sub02_08_01.html

Looking at the specifications and schematic, the original three wire thermostat included a small thermal fuse (73C-84C) as well as a 60 degree F/16.2 degree C thermostat inside the sealed black casing.  The original part has three wires:  a white wire, an orange wire and a brown wire.  The brown wire actually allows current to flow to the defrost heater when the thermostat is closed, and when the temperature in the evaporator area near the thermostat exceeds 60F, the thermostat opens and shuts down the heater.  The thermal fuse is evidently there to protect the system from a heater malfunction, and resides between the white and brown wire based on continuity testing and the schematic.

Before disassembling and reassembling the refrigerator, I unplugged the unit.

To replace the unavailable part, I purchased the components of the thermostat and made my own.

Here are the parts I used:

• Supco ML60 thermostat.  This thermostat opens at 60F and closes at 40F.  The original thermostat opened at 61.6F/16.2C and closed at 37.7F.  (a 22.3F/5.4C degree range).  This was available for $2.95 at McCombs Supply.

• Supco SL247 clips for attaching the thermostat to the evaporator tubes. ($2.70 for a pack of 3 at McCombs).

• A Microtemp 73C thermal fuse on Ebay.  ($2.50)

To make the part:

1. Take a picture of the original installation



There is a thermostat and thermal fuse inside the sealed black casing of the unit.  The brown wire goes to the heater and can receive current from the defrost timer when the temperature is below 40F.  If the thermostat breaks and gets stuck in the open position, the heater never turns on even though the defrost timer advances.  That is why the evaporator ices up.  There is also a small thermal fuse between the white wire and the thermostat inside the black casing to protect the system. 

2.  Cut off the two-conductor, white plastic connector with orange and white wires, leaving about 3 inches of wire coming out of the connector.

3.  Slide a piece of medium size heat shrink tubing over the white wire, from the white connector almost up to the end of the wire cut.  Strip away the insulation on the white wire, and crimp it to one side of the new thermal fuse using a small size crimp connector suitable for 16 gauge wire.  It doesn't matter which end of the fuse you connect to the wire.

4.  Cut off the  entire length of the brown wire from the old thermostat.

5.  On the new part, crimp the brown wire and one of the new thermostat wires to the free end of the new thermal fuse.

6.  Pull the heat shrink tubing over the new connections, and heat the ends of the shrink tubing to seal the connections.  Don't heat the ends too long, and don't shrink the tubing over the fuse or you might blow the thermal fuse.

7. Slip a short piece of heat shrink tubing on the free orange wire and crimp connect the orange wire to the remaining wire from the new thermostat.  Pull the heat shrink tubing up over the new connection, and shrink it tight over the crimp.

Here are some pictures of the new part before applying the shrink tubing:



Assembly completed before heat shrinking the tubing.  Note the thermal fuse sticking out of the longer piece of shrink tubing on the right.  This fuse was crimped to the white wire coming out of the connector.  The crimp connection can't be seen here because of the heat shrink tubing.  After all the connections were made, this long piece of shrink tubing was pulled up over the fuse and both connections at the ends of the fuse.



On the bottom are  thermal fuse connections to the brown heater wire and to the new red thermostat wire.  The red wires are the new thermostat wires.   The top wire connection connects the other new thermostat wire to the original orange wire.  It doesn't matter which of the new thermostat wires get connected to the fuse end or the orange wire.





Finished part with connections covered and heat shrink tubing ends sealed.  You can add some silicone sealant to the ends if you want.

To finish, I attached the new thermostat to the evaporator tubing using one of the new clips.  Route all the wiring towards the back of the freezer box, behind the existing evaporator tubing. Plug everything into the connectors in the evaporator area.  I reassembled the freezer compartment, ice maker, etc. and plugged in the refrigerator.

Here's a picture of the new part inside the freezer/evaporator area:



New installed thermostat and thermal fuse unit with wires tucked behind the copper evaporator tubing.  The new thermostat just clips to the tubing where there is covering to prevent a dissimilar metals interaction.

This fix worked for me in replacing the no-longer-available 63001599 Korean three wire thermostat.  The total cost for parts was about $15.00.   The refrigerator is now cool, and I hope to get another 10 years out of this appliance.

2/25/17 Update:  When I replaced the thermostat as described above, it did not stop ice from building up on the evaporator.  I know the old thermostat was bad because I tested it, so the work above was necessary, but it didn't completely fix the refrigerator.  The other parts that control the defrost heater circuit are the defrost timer and the defrost heater itself.  I checked the defrost timer by manually turning it to the defrost heater cycle (which shuts off the compressor) and found that it was advancing through the cycle properly.  While testing the timer, I noticed that the heater which is attached to the evaporator coils was not heating up--I couldn't feel any warmth through the back wall of the freezer.  When I took the old heater out, I noticed it had a burned spot on the glass near one end, and there was moisture inside the tube.  I definitely needed to replace the defrost heater.

When I went to the appliance parts websites to find a replacement, I faced a familiar and aggravating problem with this refrigerator.  The part I needed, AP4072093 or 63001595, was no longer available. The original  glass tube heater used in the refrigerator was 24 inches in length.  I found a possible replacement glass tube heater that was about 24 inches long in the Supco SH267 part, but I noticed it was rated at 500W.  The tag on the inside of my Admiral LTF2112ARW refrigerator said the unit uses 3.8 amps, or 456W at 120V.  I really didn't want to get a heater over 450 watts, so I found the Supco SH320 Tube Heater that is rated at 450 watts. 

The only problem with this Supco SH320 heater is that it is shorter (20 inches) and has a thinner glass tube diameter than the original.  Nevertheless, I bought the heater.  When it arrived I cut the plastic electrical connectors off the old heater and soldered them onto the new Supco SH320 heater, using heat shrink tubing to protect the soldered splices.  The original defrost heater simply hung from the bottom of one of the lower evaporator tubes by two small steel clips.   I was able to remove those clips and move them a bit toward the middle of the evaporator unit so they would  support the new, shorter heater.  You have to kind of fit the clips into the aluminum fins that fill the spaces between the evaporator tubes and make sure the clips snap onto an evaporator tube.  I also crimped the clips a bit so they would grab the thinner diameter tube.  I put in the new heater tube, centering it in the width of the evaporator unit, and reconnected the wiring.

The refrigerator has been running for about a month now with no frost buildup on the evaporator tubes.   The Supco SH320 450W heater is adequately keeping the evaporator free of frost, with the thermostat shutting it off when the temperature rises above 60F in the evaporator area.  Fixing the frost problem required both a new thermostat and a new defrost heater, and has kept this 10 year old refrigerator alive.  The total cost for the parts needed to construct a new 3 wire thermostat and using the new Supco SH320 quartz tube heater came to about $35, including shipping costs.