Hello,
The compressor is running non stop freezing the Evan coils. After thawing the coils, the compressor seems to cycle normally for a few days, then the coils freeze again. Need to that every few weeks... Not sure if the problem is the defrost thermostat (it looks ok) the thermistor of the control board. Any help to diagnose would be appreciated.
Thank you,
mark.

Thanks for your help, looks like it is the board since the defrost element heated up nicely. Is this board located under the control panel in the refrigerator? Will the defrost cycle stop automatically?
Thanks again for your help.

A quick note: Anytime you change the water pump on your vehicle, you should change the thermostat too. As for your refrigerator, the defrost bi-metal thermo thermostat is a ON/OFF type switching device, it operates once every 8 hours or so, or approximately 3 times per day. It is usually rated for 10,000 lifetime cycles, so that equates to about 9 years and 1-1/2 months. If you don't enjoy taking the freezer food out and taking the racks and side hardware off to remove the back panel then change the bimetal thermal switch every 10 years, or have it fail on the 11th, 12th, or 13th year and lose out on spoiled food. A good back up switch that I use to piggy back as a troubleshooting tool is the OEM W10392132 that sells for $4.55, it has been replaced by a $40 one, but since I purchased 50 of the OEMs, that's what I've been using for years and I have yet to have one fail. Though this may not be your problem now, it will be in the future, but from your description, it certainly sounds that way, and even if it isn't, change it as you would a thermostat when you change your water pump. Call it preventative maintenance. As you state that your compressor is always running that means that your defrost heater is never running. What controls the switching is your first hint then work back and outwards from there. Do processes of elimination. Start with the forced defrost. Do what is easiest and where you will get the fastest reward. Without extended tools and wiring diagram analysis, you will take a bit longer to come to a solution, but beware and don't start guessing and replacing because that can be expensive and annoying. First do your diagnosis then confirm the diagnosis then confirm that the part is bad with proper testing then do the repair then confirm the repair.