[Pumanator]

My side by side builds up ice in the bottom of the freezer and some in the coils. MSD2436GRW is the model number. Have read some of the other posts and see timer, defrost switch, heater and I also have read something about a mother board that can go bad. Where do you look for the 3 items that are the main culprat of this problem. Also how to you test these items so as not to "parts swap" the problem

[hvac1000]

Heater located in the freezer along with the defrost bimetal/termination thermostat. Test to be sure power is applied during the defrost cycle. (115/120 volts will be present UNLESS the defrost timmer is defective) Also the heater will ohm out and not be open and the defrost bimetal/termination thermostst will be closed if its temperature is below freezing but you need the manual for the exact operating temp of the defrost bimetal thermostat since many different ice boxed use different settings.

My solution has always been to replace all three parts to prevent service call backs or at least replace the timmer and bimetal thermostat if the heater tests good.

The location of the timmer could be almost anywhere since all units are different but here is a location for pictures on the right side.

[hvac1000]

Also see all the diagrams here

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[Pumanator]

Found that it has a motherboard for defrosting. Does that take the place of the time and how do I test

[hvac1000]

Item 13 on this page says your unit has a defrost timmer in your unit.

Part Advantage :: Part Search

It says your unit has a fountain control circuit board but not a defrost circuit board. I guess it is possible you have a circuit board but the drawing does not show it.

[Pumanator]

Yes, you are correct... I have been under the false assumption the I had a motherboard and actually that's a good thing I don't so I just need to check the usual suspects.

[hvac1000]

I try to be correct but you never know when they will sneak something different into an appliance.