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Parts for Maytag MSD2660KES Refrigerator - AppliancePartsPros.com

See the attachment for the tech sheet.

I am assuming that the evaporator/freezer fan is running normally.

Your unit does not use a defrost board.
Defrost is controlled from the main control board (item 23 in section 01).

When it happens again, remove the cover in the freezer so you can inspect the evaporator/freezer coils.
If heavily covered/clogged with ice/frost then it is a defrost problem.
Do not defrost them.
Force a defrost cycle (see the tech sheet)
Check if the defrost heater comes on.
Be careful that you do not burn your fingers.

If it comes on then probably the control board is shot.
it is not programming a defrost when it should.

If it does not come on.
Unplug the unit.
Check the defrost thermostat. It should be 0 ohms when frozen.
Note that it opens just above freezing so should be frozen.
Also if it is deformed/bulged replace it even if it measures OK.
Check the defrost heater, should be around 30 ohms (I think tthis is a 26 cubic foot unit)
If both are OK then either there is a wiring problem between the control board and the heater combo (unlike;ly) or the control board is shot.