Refrigerator Defrost Problem Diagnostics
If your refrigerator has a defrost problem this page will help. Refrigerators
have what are called evaporator coils and these coils are located inside the
freezer. When the compressor runs, the evaporator coils become very cold (way
below freezing). Also when the compressor is running there will be a fan that
pulls air through the evaporator coils to cool down the freezer and the fresh
food section. When this happens the moisture in the air will freeze and stick to
the evaporator coils. Every so often, the refrigerator has to go through a
defrost cycle to melt this ice that continues to build up on the coils from the
moisture in the air. If the refrigerator has a defrost problem and will not melt
the ice, it eventually builds up to the point that it blocks airflow. To begin
with, it will seem like the freezer is ok but the fresh food section will start
to fail. If the problem is not resolved the freezer will start to thaw as well.
It can take up to a month to get to this point.
If your refrigerator is not cooling and you suspect you may have a defrost
problem, it is easy to confirm. First, take a look at the evaporator cover. The
evaporator cover is typically located on the back wall of the freezer. If there
is a defrost problem there will be thick ice on the evaporator cover. If there
is thick ice forming on the evaporator cover, remove it. Once the cover is off,
view the evaporator coils and if they are completely covered with ice/frost (see
picture below) then you have a defrost problem.
Types of defrost system
The next step is to determine which type of defrosts system your refrigerator
has. There is two basic types of defrost systems: one is mechanical defrost and
the other is adaptive defrost. Mechanical defrost systems use a mechanical timer
to initiate a defrost cycle every so often. Most defrost timers will run a
defrost cycle every 6, 8 or 10 hours for 30 minutes. Under most circumstances it
is unnecessary to run a defrost cycle as often as a mechanical timer; therefore,
mechanical timers are inefficient, which brings me to adaptive defrost controls.
Adaptive defrost controls use an electronic control to determine when the
refrigerator needs to run a defrost cycle. This is much more efficient because
with adaptive defrost systems, defrost cycles can be up to 48 hours apart;
therefore, there is no wasted energy on an unnecessary defrost cycle.
Now
that you know about the different defrost systems, I will tell you how to
determine which of the two your refrigerator has. First, locate the defrost
control. Common places to look for defrost controls are near the temperature
control in the fresh food section, behind the toe plate near the bottom and
sometimes on the back of the refrigerator. Check to see if your refrigerator has
a mechanical timer or an electronic control. GE side-by-side refrigerators do
not have separate defrost controls; they have a main board that controls every
aspect of the refrigerator. There is more on this type of defrost system below.
Mechanical defrost system
If your refrigerator has a defrost problem and you determine your
refrigerator has a mechanical defrost system, follow the steps below to
determine which part you will have to replace to repair the problem.
1. Locate the timer and slowly turn it until the compressor and fans turn
off. By doing so, you have manually placed the refrigerator in a defrost cycle.
2. If you haven’t done so, remove the back wall of the freezer to access the evaporator coils. Wait 10-20 minutes to see if the defrost heater has come on. If the heater has come on you will either see it glowing red or you will hear the sound of water hitting a hot surface.
If the heater comes on there is no need for further diagnostics; you
will need to replace the defrost timer. Unplug the refrigerator and melt the ice
or let it melt on its own. Note occasionally this will be a false diagnosis
because sometimes the defrost thermostat will be the problem, yet the heater
will still come on when you perform this test, so to be sure you may want to
replace the timer and the thermostat. If the heater doesn’t come on continue to
the next step.
3. Unplug the refrigerator and melt the ice or let it melt on its own.
4. Once the ice is melted, check the defrost heater with an ohmmeter. If it is open or grounded out, replace it. If the heater checks ok replace the defrost thermostat.
Below is a picture of a bad defrost thermostat, so if yours looks
like the one in the picture there is no need for further diagnostics. Just
replace the thermostat but note that if the thermostat doesn’t look like the
picture it can still be bad so you will need to check it.
Notice how the plastic cap on the one on the right is coming apart from the metal thermostat. This is an indication of a bad thermostat that must be replaced with no testing necessary. However, the one on the left looks fine however you should still test it because it still could be bad.
Adaptive defrost system
If you determine that your refrigerator has a defrost problem and it has an
adaptive defrost system, this section will help.
1. Since you cannot force the refrigerator into a defrost cycle on most models, go ahead and unplug the refrigerator.
2. If possible check the defrost thermostat before the ice is melted. If you don’t, you will not be able to check the thermostat because it will have to be cold at the time of testing. If the thermostat is below 40 degrees it should check closed with an ohmmeter and if it is open, replace it.
3. If the thermostat isn’t bad, melt the ice and check the heater with an ohmmeter and if it is open or shorted, replace it.
If the heater and the thermostat both check ok, replace the adaptive defrost
control.
Note: This section applies to all GE side-by-side, some GE top freezer
models, and some GE bottom freezer models with main control boards. If the
refrigerator has a main control (with the exception of French door models) this
section will show how to diagnose a defrost problem.
Below is a picture of a
main board that will be located on the back of GE refrigerator models covered in
this section.
GE electronic refrigerators have a main board. This main board
controls every function from defrost, fan speed, the compressor and even
compressor speed. To control the defrost cycle, the main board monitors things
such as how many times and how long the door is open, as well as length of past
defrost cycles to adjust to environment and usage and adapts.
This ensures that the refrigerator doesn’t defrost too often while at the same time ensuring that it defrost enough to maintain the evaporator coils. There are four things that can cause a defrost problem on a GE electronic refrigerator and they are the main board, the defrost thermostat, the evaporator thermistor and the defrost heater. Follow the directions below to diagnose which of the four parts are bad.
1. Disconnect the refrigerator.
2. Locate the main board on the back of the refrigerator.
3. At the bottom of the main board you will see two plugs: one is blue with
three wires and the other is white with nine wires, disconnect these two plugs.
From these two plugs you can check the defrost heater and thermostat circuit
with an ohmmeter.
4. Check for continuity from the J9 wire to the J7 pin 9 wire. Note that the J9 wire is the center wire on the blue three-wire connector and the J7 pin 9 is the orange wire on the white plug, which should be the wire that was connected furthest left. If this circuit is open skip to step 6. If the heater and thermostat are not faulty, you should get a closed circuit around 15-25 ohms, give or take. If you are working on a top-freezer or bottom-freezer you may get a higher ohm reading, (25-50 ohms) this is ok as long as it isn’t extremely high. If this is the reading you get on this test proceed to step 5. If the ohm reading is extremely high or open
click here to skip to step 6.
5. If the heater and thermostat check ok (closed circuit) you need to check
the evaporator thermistor.
Please note that this test must be done before the ice is melted; however, if
you have already melted the ice, refer to this page. It will show how to test
the thermistor after you have melted the ice. How To
Test A GE Refrigerator Thermistor
Follow these steps to test the
evaporator thermistor.
a. Locate the connector on the board marked J1 and disconnect it.
b. Using your ohmmeter, check ohms between the 5th wire and the 4th wire (see
picture below). Assuming the thermistor is covered with ice (it should be if you
have a defrost problem), you should get around 16.3 K ohms +/- 5 %. If the
thermistor is out of range, replace it.
Just as a note that most of the
time when I see a bad thermistor, it is way out of range typically it will be 2
K ohms when it should be 16.
a. Melt the ice and locate the thermostat and the heater.
b. Take a look at the thermostat and compare it to the ones in the picture
below. If it looks like the bad thermostat, there is no need for testing. Just
replace the thermostat.
Notice how the plastic cap on the one on the right is coming apart from the metal thermostat. This is an indication of a bad thermostat that must be replaced with no testing necessary. However, the one on the left looks fine however you should still test it because it still could be bad.
c. Remove the heater and test it with an ohmmeter. It should be around 15-25 ohms give or take and if not replace it. If the heater tests ok, replace the thermostat. If you are working on a top-freezer or bottom-freezer you may get a higher ohm reading, (25-50 ohms) this is ok as long as it isn’t extremely high.
If the heater, thermostat and thermistor check out ok, replace the
main board.
Once the problem is found melt all the ice and replace
necessary parts.
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