[ieajrl]

Kitchenaid built-in side-by-side freezer working fine, refrigerator not cooling. Tech replaced evaporator motor, didn't fix problem. I ordered and replaced the control board which is part of the diffuser assembly AP3109138. It worked fine for half a day or so and then the evaporator motor stopped running again. The evaporator motor works fine if you jumper power to it.
1. Is it possible to get a tech sheet for this model?
2. Any ideas on if the control board is the problem and why it is failing?
3. Is there any way to test the functions of this board?

Thanks

[Gene]

Most likely the problem with your fridge is the thermistor (#23 on the refrigerator liner break down diagram).

- Here is the tech sheets for your fridge.

- The part number for the thermistor is AP2935875


- Here are the break down diagrams for the Kitchen Aid refrigerator Model KSSS42DAX03

Good luck.
Gene.

[ieajrl]

Thanks for the quick reply and the tech sheet.
I measure the thermistor at room temperature at 1.47K ohms. Is this the right range for this model?

Also, the tech sheet suggests checking the door in the mechanical baffle. How would I check to see if this is functioning correctly?

Thank you.

[Gene]

Unfortunately I do not have the chart for the thermistor resistances but 1.47K ohms looks not enough. I believe it suppose to be much more.

The door in the air baffle operated by the control board (which you already replaced) according to the thermistor reading.

Gene.

[ieajrl]

You're right about the thermistor. Its resistance is too low and does not increase with temperature. I've ordered a new one. The fridge is working perfectly if I swap in fixed resistors to simulate the refrigerator at correct temperature or calling for cold air.

The air baffle in this model has three wires: common (white), open (white/brown) and close (yellow/red). The board is switching 115v ac with a triac; it always energizes one side or the other. When the baffle assembly gets power on the open side, it runs the door until it's open and then opens a microswitch. Same process to close. You can test by applying power to one side or the other.

[Gene]

Keep me updated, please.

Best regards,
Gene.

[ieajrl]

Gene,

My educational background is in EE. There is an obvious interaction going on between the thermistor, the control board and the evaporator motor. You could throw in the air damper unit too, but in my case, it's just working correctly.
I've created an approximation of the schematic for the the control board that you can see in the attached JPEG. The intention is pretty straightforward. There's an AC->DC power circuit on the right. On the left, two resisitor divider elements: one with the thermistor, the other with the refrigerator temperator setting, and a four element comparator that drives three SCRs. Two open and close the air damper. The third controls the evaporator motor.

When everything is working, the circuit does its job. In my case, the failure of the thermistor and (?) the evaporator motor caused diode D2 to short. With D2 shorted, nothing works. My refrigerator is working because I removed and tested diodes D2 and D4; since D4 was working and D2 was shorted, I have replaced D4 and not D2. In addition, I have added a series resistor between the diode bridge and the big cap. It is my opinion that not having a series resistor in a simple zener diode regulator like this is an oversight that leads to diode failure. As a side note, you should never put zeners in parallel as they did in this circuit.
With one zener and a series resistor, the board is working perfectly in my refrigerator. As you know. I don't have a working thermistor, but I'm simulating one by swapping in fixed resistors. So far, everything is working as I would expect.
Tomorrow, I'll receive the replacement thermistor and see if I'm back to a fully functional, automatic system. I'll let you know how it goes.

-- Peter

[Gene]

Hi Peter,

No problem! Just let me know if you have any other questions.

Gene

[richappy]

I also have a BSEE degree.When I worked for a hospital equipment co. we would life test designs, seems like on top of a shoddy circuit design, they never fully tested their product. Probably nobody scoped things to check for potentially damaging transients and race conditions that over stress semiconductors.
The schematic is unreadable, so have no other comments.