I have a maytag MSD2556AEA refrigearator and the coil freezes up. I've replaced the the defrost timer and the heater and it still freezes up.

The timer should last a lot longer than that, but I have received bad ones right out of the box. Depending on model year, the full current of the compressor and the defrost heater are present in the defrost timer contacts. The defrost heater should be checked with a volt-ohm meter if continued icing takes place. The defrost heater will have a positive ohm reading if it is okay. If the meter reads infinity or 0.0 ohms, the heater is bad.

Hello,

Yes there is a defrost thermostat that is clipped to the top of coil in the freezer,it's round.about the diameter of a quarter and a inch or so thick,usually metallic base with a plastic top,remove the two wires to it WHEN IT'S COLD should have contintuninty(zero ohms resistiance) when testing witha meter, if it checks to be good when cold and the heaters are new,the only part left that will make the evap. coil over frost is depending on your model the defrost timer or electronic defrost control, commomly called on the Maytag brand(s) the adaptive defrost control.

Good luck.i hope this helps

Gene

DEFROST PROBLEM
The evaporator coil behind the cover on the back wall inside the freezer will ice up under normal conditions. Every 8 to 10 hours for around 20 minutes the defrost timer (or in most newer models the electronic adaptive defrost control) will turn the defrost heater on to melt the built up ice. There is a defrost thermostat which prevents the heater from overheating the freezer by breaking the heater circuit when the temp reaches close to 32 degrees F. The entire cooling system shuts off during the defrost cycle and starts back when the timer advances through the cycle.

If this ice is not melted it will continue to build up until the air can't flow over the coil to circulate the cold air through the freezer and into the fridge. The temperature change in the fridge is usually noticed first followed by the freezer.

If the defrost thermostat is bad, it can prevent the heater from coming on OR it won't turn the heater off when it gets too warm. It is clamped to the evaporator coil at the top to sense the temp. If it appears to be misshapen it is bad.
With an ohm meter it should show continuity when cold and none when warm.
You can also bypass(disconnect the two wires plugged into it and twist them together) the thermostat to see if the heater comes on then. If it does then you know the thermostat is bad and needs replaced.

The defrost heater is located on the evaporator. It is in a tube which is at the bottom and can also go up the sides of the evaporator. On some types you can see a burnt spot if it's bad. With an ohm meter it should show continuity from end to end when disconnected from the wiring in the freezer. You can also test the wiring for voltage when it's in the defrost mode.

If you have a defrost timer you can test it. It can be located under the fridge behind the kick panel on the front. Some are in the fridge with the controls at the top. You can turn the defrost timer till it clicks and everything shuts down. The heater should now come on. If it does, replace the timer because that means the timer is not running. If it doesn't, check the heater and defrost thermostat. Turn the timer again till everything starts back up to end the defrost cycle.

If you have an adaptive defrost control instead of a timer, replace it if the heater and thermostat test good. It is located in the fridge with the controls in some models and on the back in others.

Defrost problem: 3 components. Defrost Heater. Timer (circuit board or motorized) & Thermostat.
Remove cover on the inside back wall (usually 6 screws). Note frost pattern. (bottom of evaporator coil)
Put refrigerator into defrost cycle and note the defrost heater come on, or not. (careful heater can glow red hot)... Unplug Frige and test defrost components. Replace bad component... Refrigerator should defrost every 8 hours. when the cycle slows or quits the freezer will freeze over the evaporator coil and no air flow = no cold air...

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Check out these tips...they can help you figure out whats going wrong with your refrigerator and why it is not cooling

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heatman101

the timer tell it when to defrost but the defrost terminator and heaters must be working . ( you probley need the heater. and if so replace the terminator also .. mm

sounds like a defrost problem. defrost system consists of defrost timer or defrost control board,defrost heater,and defrost thermostat. most maytag sxs refrigerators have a circuit board in charge. part no.61005988 adc board.change the board and yer in business...

How to check everything
http://www.acmehowto.com/howto/appliance/refrigerator/refrigerator.php

If the evaporator coils behind the back panel of the freezer are icing up because of auto defrost failure that will stop the circulation of cold air and eventually affect the freezer too.

check defrost timer, defrost heater, defrost thermostat. In most newer models the timer has been replaced by an electronic control board. If the heater and thermostat are ok it’ll be the control.

You can turn the defrost timer till it clicks and everything shuts down. The heater should now come on. If it does, replace the timer. If it doesn't, check the heater and defrost thermostat. Turn the timer again till everything starts back up to end the defrost cycle.


Or make sure the condenser fan underneath the unit is running.

Defrost heater or heater safety thermostat or defrost timer faulty.