Multimeter: Testing the Refrigerator Parts
Caution: Unplug the refrigerator! These tests are conducted with the unit NOT being plugged in, i.e., NO ELECTRICITY!
Unplug the electric cord!
Using a Multimeter
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 [battery(ies)]! You will need a multimeter to test your refrigerator parts!
You can get a cheap meter if this is a one-time-use item. Check out a few ads in a magazine or your favorite websites to compare prices and features.
Some cheap units are not accurate, but can do a simple continuity test on your refrigerator parts. Compare prices before you buy...will you use this one time or will you use it again? [You can use the multimeter to test batteries, switches and other appliances you might have.]
This is a digital multimeter.
Different multimeters may have different features.
Read the instructions that come with your multimeter for specific information.
Meter Readings
Refrigerator Defrost Heater Element
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, the heating element is bad and should be replaced.
Refrigerator Defrost Thermostat (bi-metal contact)
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!)
Note:
Heater and Thermo-one unit in a series
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.
Close-up of Plastic Connector
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.
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.
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.
Switch red probe to left or white/pale green wire slot
The defrost thermostat can be tested by inserting the red probe in the white/pale green wire to the left. Warm, it will open (no continuity) and cold, it will be closed (continuity). You can test warm and cold as indicated above.
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.
Adaptive Defrost Control
The adaptive defrost control basically does the same job as a defrost timer and more. Like 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.
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.
Testing the adaptive defrost control is different than testing a defrost timer. If the defrost heater and defrost thermostat test out okay, replace the adaptive defrost control.
There are field tests that a trained technician can do on the ADC, but since the refrigerator must be plugged in, and you are dealing with live voltage, I will not go into details. As mentioned above, if the defrost heater and defrost thermostat test out okay, replace the adaptive defrost control.
You can test the defrost timer for continuity. Set the multitester as instructed above. Place one of the multitester'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 multitester 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.
Defrost Timer
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 multitester to test the terminals again in the same manner as described above.
*Notes: Read the directions on how to use your multimeter that comes with your multimeter (for specific multimeter information and symbol meanings).
Ω = ohms
= audible continuity
Zero Ohms: This means you have zero resistance, but it also means you have continuity. "00.0"
Continuity: This means the circuit you are testing is complete. A straight piece of wire represents a circuit with zero or near zero resistance. If you measure resistance of that circuit, the meter would indicate zero ohms, and you have continuity regardless what scale you have selected. If you were to cut that wire, you no longer have continuity.
Open Circuit: This means you have infinite resistance and no continuity. Infinite (infinity) means the open circuit represents so much resistance the meter cannot measure it. No beep, no measurement.
Closed Circuit: This means the circuit you are testing is complete, i.e., you have continuity.
Infinity: No beep, no measurement. "0L." (open loop) or "1" on some meters.
Refrigerator Defrost Heater Element
and the
Refrigerator Defrost Thermostat (bi-metal contact)
Located in the freezer compartment behind the panel.
See repair section for information on how to remove and replace.
A word about the ADC:
I just replaced the ADC in an eight-year-old refrigerator. In this model, it is located inside the refrigerator compartment above the temperature control levers and towards the rear. Enlarge the photo and look in the upper right corner area in this photo.
Worth mentioning: You may be one of the unlucky ones, who gets a defective ADC right out of the box or maybe the wrong ADC! Check your parts person, i.e., make sure you repeat the brand/model number of your refrigerator when ordering in person or by phone to try to make sure you get the correct ADC. I like to order online because I get to compare prices from different parts suppliers. When ordering online, double check your numbers!
Defrost Timer
In many cases, the ADC is the culprit when the defrosting action stops. The newer ones have a LED light that helps diagnose problems. The bad part is that you still need to take the refrigerator light/control panel off and then remove the ADC cover to see the light!
Disconnect!
ADC location in refigerator compartment (on this model)
Refrigerator Parts--Defrost System
Heater, Thermostat, Timer/Adaptive Defrost Control
Multimeter: Testing
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.
Compare prices before you buy:
- Multimeters vary in prices.
- Get the best deal for your specific needs:
- One time or multiple uses over the years. (Cheap vs.Expensive)
Copyright@2010
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 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].
*(See notes at the bottom of this page for more information on ohms, continuity, circuits)
Auto-Ranging Multimeter
Switched Multimeter
(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.
(right click to enlarge)
Multimeters come in different sizes, colors, and shapes. Multimeters can have different features and levels of sophistication. Some have the leads integrated and some have plug-in leads.
Use the continuity setting
Integrated Test Leads/Probes
If it is not a defrost problem:
Compressor and
Related Parts-
For Technicians Only
If it is not a defrost problem:
Compressor and
Related Parts-
For Technicians Only