Freezer defrosts too long.

Sounds like your defrost cycle has failed. Since the unit is running fine for a while before warming up, this can rule out your circulating fan. Your defrost cycle is operated by a defrost timer or your motherboard depending on the age of your refrigerator. When your refrigerator goes into defrost, it turns on an electric heater that melts the ice from your coil in the freezer. When your defrost time or electric heater fails, it allows ice to build up on the coil in your freezer which blocks airflow which causes your cooling compartments to not maintain temperature. Hope this gives you an idea what to look for and a guide on where to start looking

You have a 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.

. 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.

This is what is happening. All "frost free" refrigerators are not truly frost free. The cooling comparment elements frost up with moisture from the air. Every 6 or 8 hours or so the fridge shuts down. then . small electric heaters fitted into these cooling elements melt the frost away. The water goes down a tube into what is called a drip pan mounted underneath the fridge. If the drain tube clogs with a piece of paper, or food or algae. The water from the frost melting stays in the pan because the drain is clogged. So each time the fridge defrosts, it builds up ICE not frost and eventually it completely clogs with a block of ice.
The other thing that can happen, is that the timer that controls this cycle fails and the heating elements never turn on. The the fridge then clogs with frost. The fridge will clog with frost if any of the following parts fail. The defrost thermostat which opens up the heater circuit when the coils reach
around 40-50 degrees, the defrost heaters mounted in the cooling coils, or the defrost timer fails.
If your fridge works normally after this, then the drain hole was clogged and you unclogged it. If it gets colder and colder again. Then the timer, defrost thermostat, or the defrost heaters have failed.
Hope this helps. You are welcome to write back to me and tell me what is happening with your fridge. I hope this helps, Best Regards, Mark

Hello and Welcome to Fixya,

This is one of the most common problems in most of the refrigeration appliances. What’s going on here is that the condensate drain hole in the freezer gets plugged with ice. Once this happens, all the frost melted off the evaporator during subsequent defrost cycles can no longer drain and so spreads out on the freezer and dribbles down and also chokes other components. Here are the instructions that you need to follow inorder to get rid of the problem:

• Unplug the refrigerator and pull everything outta the freezer, and I mean everything.
• Remove the bottom panel inside the freezer so you can see the condensate trough in the back of the freezer.
• Notice that the condensate trough is filled with ice– all that has to be cleared out.
• Take it easy back there, delicate parts are exposed– don’t start hacking at it with an ice pick because there are chances that you’ll just end up puncturing the evaporator and you’ll turn a simple, inexpensive repair into a majorly expensive one.
• Use hot water to drain all the frosted ice that is visible.
• Re-place all the units removed during the process.
• Once all the ice is cleared away and the condensate drain opening is cleared, you are done.

Best of Luck,

Please do rate my solution, If found helpful.

Regards.

When the heater comes on for defrost behind the rear freezer panel , it gets red hot . The defrost thermostat ( bimetal ) , cuts the heater off , when it reaches 140 degrees for new (2000 - 2009 ) and 55 degrees for older refrigs . When this temp is reached at the top of the coils , the lower portion will be hotter due to being closer to the heater . The frozen food in the freezer , is what keeps the temp down in front of the rear freezer panel . No food in freezer , the hotter the freezer section will be .

Your evaporator coils frost up in normal use and every eight hours or so the entire unit shuts down and the defrost heater comes on to melt the frost. This cycle last about 20 minutes. The melted frost drips into a drain pan and through a drain tube to the drain tray under the freezer/refrigerator where it's evaporated by the condenser fan.

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.

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

Yes it is supposed to. Your evaporator coils frost up in normal use and every eight hours or so the entire unit shuts down and the defrost heater comes on to melt the frost. This cycle last about 20 minutes. The melted frost drips into a drain pan and through a drain tube to the drain tray under the freezer/refrigerator where it's evaporated by the condenser fan.


If it seems to defrost too long and start thawing the contents then the defrost thermsotat may be bad. It's purpose is to stop the defrost heater when the temp reaches around 32 degrees. If it doesn't work the heater will stay on for the entire defrost cycle and possible melt things.
Check here for how to check it and where it is. http://www.acmehowto.com/howto/appliance/refrigerator/refrigerator.php

Unit is obviously in defrost too long. Verify defrost clock operation and time setting.You may reduce the amount of minutes per cycle that defrost is actually called on for . 20 minutes should be adequate if you are defrosting more than once per 24 hrs. Defrost clock should have "X" terminal which will terminate defrost once evaporator coils reach a certain temp. It is controlled by a three wire defrost thermostat relay(clixon) attatched to the actual coil in the event this coil reaches 50 degree,the clixon triggers the "X" wire in the timer and terminates defrosting.It figures if it reaches 50 degrees,it must then be free of ice on the coils

Check out partselect.com. need to replace defrost timer and defrost thermostat. good luck.