[dalton95070]

I seem to have a failure of the defrost controller. This happened once before, about 10 years ago, and the symptoms are similar: back of the freezer is all iced up, but temperature is high in refrigerator and freezer. I have ordered the controller board (still have the old, dead one right here).

While waiting, I defrosted by hand, thinking this would put me in good shape for a few days at least. But it didn't. After about 12 hours quite a bit of snow and ice had built up again, but the overall freezer temp was too high to freeze any liquid. Refrigerator temp was high too, around 60F.

Is something else wrong besides the defrost cycle? How could the evaporator be cold enough to form all that snow and ice, yet not get the rest of the box cold?

Also, what makes these defrost control boards go bad, and is there any chance of repair? The board isn't complicated: all through-hole components, only one IC (a PIC16 microcontroller), two transistors, some resistors, capacitors and diodes, and a big relay switch. There are no signs of injury or damage to anything on the board. I would guess the relay, having nothing else to go on. Advice?

[Simon / APP Team]

Hi.

Open the rear cover and look at the evaporator coils. If they blocked with ice evenly - then it's a defrost problem.
Make sure the evaporator fan is working.
The defrost system has two more parts which you need to check before replacing the defrost control board.
The defrost heater and defrost thermostat may be checked with continuity test.
Remember that the thermostat must be ice cold when tested.

Here are the breakdown diagrams and Replacement parts for Maytag MSD2758DRB REF - SXS/I&W | AppliancePartsPros.com

The defrost heater and thermostat Part number: 61006199

The safest way of defrosting the evaporator is to unplug the unit for 24 hrs.

The snow forming on the evaporator is blocking the air flow and that is affecting the temperature.
Regarding the defrost control board.In a lot of cases it's the relay. But there is no instructions available on testing or rebuilding it.

Good luck. Post the results.

Simon.