Using a Multimeter

Multimeter:  Testing Refrigerator Parts

Test to see what refrigerator parts you might need!
You will need a multimeter to test!
An inexpensive one should work for a few simple tests.
*(See notes at the bottom of this page for more information on ohms, continuity, circuits)

defrost thermostat

can be tested by inserting the red probe in the white/pale green wire to the left.  Black probe stays in the middle slot. 

     Warm, it will be open (no continuity) and cold, it will be closed (continuity).  You can test warm and cold  as indicated above.

On this refrigerator, the heater element and defrost thermostat are sold as one unit, so if one is defective, the whole unit must be replaced.  (Don't try to save a few cents by splicing.) Some  defrost thermostats may be separate, requiring only that item  to be replaced.  But consider the cost, and decide whether to replace them both while you have the freezer cleared and opened. 
     A defective defrost thermostat can prevent the defrost heater from turning on or it could allow it to overheat.  During a defrost cycle, the defrost heater causes the bi-metal alloy in the switch to warm.  As it does, it opens the circuit.  As the bi-metal cools, it makes the circuit close.

     Using the multimeter, at room temperature the defrost thermostat should indicate an open circuit, i.e., shows no continuity.  When cool, the defrost thermostat closes the circuit, i.e., continuity.  This allows the defrost heater to heat, when the ADC or defrost timer completes the circuit when conditions indicate a defrost is needed.

     You can test it when cool by using some ice in a plastic bag to make it “cool.”  No ice?  Use a can of gas duster (computer keyboard cleaner) turned upside down and spray the thermostat with a few shots to make it cold. 
(USE EYE protection, i.e., safety glasses and keep your fingers out of the way!)
Switch red probe to left or
white/pale green wire slot
Refrigerator Defrost Thermostat  (bi-metal contact)
     The black wire is connected to the defrost heater element, and the middle white wire is connected to the heater element (splice). 

If the reading is zero or infinity (no continuity, no beep) the heating element is bad and should be replaced.
     Test the

refrigerator defrost heating element

for continuity using a multimeter.  Set the multimeter to the continuity setting. Some multimeter’s will display an actual number when in continuity mode, while others do not.

     Place a probe on each terminal.  The multimeter should beep and/or display a reading somewhere between zero and infinity. 
If the meter indicates an open circuit (no continuity, no beep) or if the reading is zero or infinity --"0L." (open loop), the heating element is bad and should be replaced.
Put red probe in black wire slot, black probe in middle or white slot
     I have removed the defrost heater and defrost thermostat assembly from the refrigerator to give you a better view. You can perform the test while the assembly is installed, simply unplug the plastic connector.
Refrigerator Defrost Heater Element
     Unplug the plastic connector at the top of the coils (near the thermostat) by squeezing the connector lock handles with your index finger and thumb while gently wiggling the connector. Do not pull by holding the wires !

Test the defrost heater element and defrost thermostat by placing the multimeter probes in the two slots on the plastic connector as indicated in the next photos.
Close-up of Translucent Plastic Connector
heaterelement and thermo
Heater and Thermo-one unit in a series
Note: On the model used in this article, the refrigerator defrost heater element and the thermostat are sold as one unit and are connected in a series.
Located inside the freezer compartment behind the back wall panel.
See replace section for information on how to remove and replace.
If it is not a defrost problem:
Multimeter Testing-
Compressor and
Related Parts-
For Technicians Only
Testing the Defrost Parts

Refrigerator Defrost Heater Element

and the

Refrigerator Defrost Thermostat  (bi-metal contact)

Adaptive Defrost Control (ADC)
The adaptive defrost control basically does the same job as a defrost timer and moreLike the defrost timer, it shuts off the refrigerator cooling devices and redirects the power to the defrost heater for the defrosting cycle.  It then redirects the power to the compressor and fans to come back on when the defrost cycle is over.  Some also record and make calculations to help make the cycle more accurate.
     If you need to locate the ADC  in your refrigerator to check or replace it:  Here are step-by-step instructions on how to locate and replace the ADC.  

Defrost Timer

     You can test the defrost timer for continuity.  Set the multimeter as instructed above.  Place one of the multimeter's probes on the common terminal.  It should be labeled 3 or C.

     If none of the terminals are labeled, you can locate the common terminal by determining which terminal coincides with the white wire in the connector plug. With one multimeter probe touching the common terminal, touch the other lead to the other three remaining terminals, one at a time. Testing the first pair should produce a reading of zero, or near zero, indicating continuity.

     The second pair may also result in a reading of zero or near zero.  Testing the third pair of terminals should produce a reading of infinity.
     Locate the defrost timer advancing screw *(timer switch) and turn it in a clockwise motion until it clicks.  Depending on the timer (there are many styles), you can usually put a flat edge screwdriver in the slot to turn it (see top left of photo circled in red).  Use the multimeter to test the terminals again in the same manner as described above. 
Defrost Timer
Refrigerator Parts
Multimeter:  Testing
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Have you changed all 3 parts, have them installed correctly--but still have the same problem?
electric shock
    The defrost timer is similar to a clock, and if the motor that advances it fails, the defrost cycle will not be started, or maybe it will stay in defrost and not go back into the cooling mode.   [How to test the defrost timer coming up below in a few paragraphs]

     Test the

adaptive defrost control

by eliminating the other two possible problem parts.  Some waste time by trying to "test" and "jump" the ADC terminals to see if the ADC is bad.   This can be dangerous because you are working with a "live" (energized) circuit--you can get SHOCKED and possibly damage the ADC and other parts.  This is easier--Remember: There are three (3) main things that can go bad with the defrost system.  Two are relatively easy to access, test and replace--the defrost heater and thermostat.  If the defrost heater and defrost thermostat test out okay, replace the adaptive defrost control.   Start with the easy parts!

     The problem will most likely be with one part.   However, several parts can go bad at once, (e.g., power surge, shorts, age).  Start with the easy parts!
Defrost Timer and ADC are tested differently
probes touching
Note: Testing Defrost Heater, Defrost Thermostat, ADC,  and Defrost Timer on this page.

Also, see Compressor section for testing compressor and related parts.
For Technicians Only
Back wall panel removed
Heater Element
(right click to enlarge)
     In this test, one of the pairs of terminals should produce a reading of continuity.  At least one pair, but maybe two, should produce a reading of infinity.

     Please note that a pair of terminals that demonstrated continuity in the first test should now demonstrate infinity.  Also, a pair of terminals that demonstrated infinity in the first test should now demonstrate continuity.  If not, and the defrost heater and defrost thermostat test out okay, replace the timer.
Privacy Policy and Disclaimer
Multimeter Testing-
Compressor and
Related Parts-
For Technicians Only
Integrated Test Leads/Probes
Switched Multimeter
Auto-Ranging Multimeter
Multimeters come in different sizes, colors, and shapes.  Multimeters can have different features and levels of sophistication.  Some have the leads hard-wired to the unit and some have plug-in leads.

Read the directions on how to use your multimeter that comes with your multimeter (for specific multimeter information and symbol meanings).

     = ohms

      = audible continuity
sound symbol
This is a multimeter>
     You can buy an analog multimeter or a digital multimeterYou can get an inexpensive meter if this is a one-time-use item. You can use the multimeter to test batteries, switches and other appliances you might have.   Check out a few ads in a magazine or your favorite websites to compare prices and features.
    Some tests do require an accurate reading.  Some cheap units are not accurate, but can do a simple continuity  test on your refrigerator parts.  
     A multimeter is an instrument used to check for voltage, resistance or continuity of electrical components and small amounts of current in circuits.  It has its own power source, i.e.,a battery or batteries! 
Caution:  Unplug the refrigeratorThese tests are conducted with the unit NOT being plugged in, i.e., NO ELECTRICITY!
electric shock
Unplug the electric cord!
Note:This is inside the freezer compartment from the front!
NOT the back of the refrigerator!

Meter Readings

     In electrical applications, when an electrical circuit is capable of conducting current, it demonstrates electrical continuity.  It is said to be closed  because the circuit is complete.  
     Test the multimeter  (Use the continuity setting) to ensure that it is working properly by turning it on and touching the probes together - the meter should read zero.  An indicator light might flash or a beeping sound  might be heard, indicating a closed circuit.  [The meter "beeps" so that you can probe for continuity without constantly looking over at the meter.]  When the probes are not touching anything, the multimeter will read infinity, showing that the circuit is open [no beep].
sound symbol

Adaptive Defrost Control or Defrost Timer

     Remember, your refrigerator can have one or the other, not both! You can tell by the model number or by taking the refrigerator apart--you decide.

     I mention that here because
this model had the ADC, but someone might be working on a model with a mechanical timer.