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
- 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
- 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
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.
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