Refrigerator Defrost System: How it Works

You wake up in the morning and go to the refrigerator to get some breakfast.   When you get out the milk, juice or whatever it is you get for breakfast, you notice something is wrong.   It's not cold!   The next thing you do is open up the freezer and see if that is still working properly.   Wheeew it is.   But why?

What you probably didn't notice was that the freezer has not been going through it's normal defrost cycle.  Because of this un-noticed event going on, there has been frost building up on the evaporator coils that doesn't belong there.  After this frost continues to build up over the course of a few days to a week or so, now you are going to start to notice the effects.

  • Here is what's happening when you have a malfunction in the defrost system.
  • Air cannot circulate from the freezer(where the cold happens basically) to the fresh food section.
  •  Your refrigerator will run constantly to try to cool the fresh food section.   This will develop a new set of problems with your refrigerator.  More on that later....
  • Excess frost builds up within the coils inside the freezer.  This is what is blocking the air flow to the fresh food section.
  • Usually you will notice the icemaker will stop making ice.  Poor air flow and not quite cold enough temperatures in the freezer cause this.
  • Water will not come through the dispenser on the door.   Cold air settles,  the water resovoir will freeze.
  •  Compressor may overheat and shut off.   This is when you hear, click, click, click.   Not good
  • Ice Cream in the Freezer will start to get soft.  That's really not that bad.  lol

What can you do about this?

Let me explain the defrost system in general so you get an understanding of what is going on. The coils inside the freezer are the only part inside the whole refrigerator that "get cold".  They need to stay free from excess frost build up so that air can pass through the coils and reach the refrigerator section of your refrigerator.   Every eight hours or so,  depending on the type of defrost timer or control you have,  the compressor and fans will shut off and the machine will go into defrost mode.

When the refrigerator is in  defrost there is a heater that is tied into the evaporator coils inside the freezer that comes on.   This heater is behind the rear panel inside the freezer where the evaporator coils are located.   It melts the frost that has accumulated over the course of time.   After about thirty minutes the machine comes out of defrost and goes back to normal operation.

Now the air can continue to pass through the coils and keep the freezer frozen and the refrigerator cool and everybody is happy.

What components make up the defrost system?

Defrost Timer or ADC Board

Some refrigerators have a defrost timer.  This type works like a clock.  Every eight hours or so the machine hits the defrost spot and that's when defrost occurs

How to Test Defrost Timer Video

Some refrigerators have an Adaptive Defrost Control.  This is what makes a refrigerator energy efficient.   It varys the length of time it takes the machine to go into defrost.   So instead of the energy hogging heater coming on every eight hours, it may be 24 hours, 18 hours, 10.5 hours, who knows.    It depends on how many times you have opened the doors, how long the compressor has run.   This is good because the refrigerator may not need to go into defrost every eight hours.   Now you are saving energy.  Good Stuff

Defrost Thermostat

How to Easily Test your Defrost Thermostat Video  

This is the component that controls how long the heater stays on when the machine is in defrost mode.  Say the defrost cycle is thirty minutes,  the heater may only be on for ten of those thirty minutes on the timer controls.    On Adaptive Defrost Controls, when the heater shuts off, shortly after the machine exits defrost mode.   Basically if the heater only stays on for ten minutes, the whole defrost cycle will only be about 12 or 13 minutes long. 

Basically when the heater comes on, it starts to melt the frost on the evaporator.  Once all the ice and frost is gone, the temperature behind the panel will start to rise.   Once the temperature behind the panel rises to a certain temperature, the thermostat will break the current of electricity going to the heater.   Bam, it shuts off and prevents your freezer from becoming a sauna, or an oven.   I'm sure you get the drift.     The heater is on the bottom of the evaporator coils and the defrost thermostat sits on top of the evaporator coils.

Defrost Heater

Defrost Heater Test Video

This is the last component in the defrost system.   This one should be pretty simple.  By now if you have read this far you should already know what this does and how important is it.   Some defrost heaters are a coil of wire in a glass tube under the evaporator coils.  Works like a light bulb basically.   The other style looks like the bake element in your stove.   They both get red hot either way and melt the frost.

So what happens now?   Well the first thing you can do to get the machine running is to remove the rear panel of the freezer.   From there you will want to remove all the frost and ice that has built up.   Pouring hot water over the coils is the best method.   The water will drain out of the freezer through the drain hole in the bottom of the freezer under the evaporator coils. 

Once all the frost is gone, you could put the machine back together and it would work fine.   For a few days, until the frost has developed again due to the defrost issue.   That would only be a temporary fix.