On your model the defrost system is controlled by the board behind the console where you set the units temps. Below is a picture.


Part number: AP4366538

Here is a tech sheet and a manual
http://www.servicematters.com/m...ibrary/docs/16025629.pdf
http://www.servicematters.com/m...ibrary/docs/16026956.pdf

Try to force a defrost, see the tech sheet.
If the defrost element comes on then your defrost control board is toast.

If it does not come on, the easiest way is to use a meter and check the defrost element (30 ohms approximately) and the defrost thermostat (closed, 0 ohms when frozen, note it opens just above freezing)

If both check out OK then it is probably the board or you have a bad connection. Most likely the board.

If you do not own a meter, I would suggest you purchase a one. You can get a decent digital multimeter for under $20.00. You do not need fancy though it is nice if the leads are a couple feet long.
If it saves ordering one unnecessary part it has paid for itself and you end up owning a useful tool.
Most places will not let you return electrical parts so if you order it, you own it.
A couple things to watch when measuring ohms and continuity
1. Always remove power from the machine otherwise you could blow your meter.
2. Always disconnect at least one side of any device you are checking. This eliminates the possibility of measuring an alternate/parallel circuit path.
3. When checking for closed contacts and continuity use the lowest scale (Usually 200 ohms). Then try higher scales. This scale is 0 to 200 ohms so if the device you are measuring is 300 ohms this scale would show an open circuit which it is not, you are just measuring outside the scale's dynamic range.

There is a good STICKY at the start of this forum about it's use.

How do you know for sure if the defrost is coming on? I forced a defrost on the fridge as suggested, and i think it turned on the defrost, but i am not 100% sure. before i spend $80 on the part, is there any way to guarantee that the defrost is coming on and the issue is the circuit board? Should I unload the freezer, take off the back panel and see if i can notice the defrost working?

Denman

Sorry for the break in time. I have been doing the forced defrost (short cycle) for a few weeks now to see if i could determine the problem. I force defrost every day or couple of days and the fridge is staying cold. However, the back panel of the freezer is all frosted up and i have a feeling that the coils are a big block of ice. Does this mean that the control board is messed up or could it be that the coil heater isnt working?

Thanks