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How To Tell If The Relay Switch On A Fridge Is Bad

Dec 01, 2016

If your refrigerator hums loudly, dims the lights, trips a circuit breaker or blows a fuse every time it tries to start, the problem may be a malfunctioning start relay on the compressor. The purpose of the start relay is to connect the start winding in parallel with the run winding to provide the extra torque necessary at start-up and then disconnect the start winding after the compressor reaches operating speed. Start relays are easy to test and inexpensive to replace.


Assemble your capacitor discharging tool. Attach one of the alligator clips from each of the jumper wires to the leads on the 20,000 Ohm wire-wound power resistor. Attach the other alligator clips on the jumper wires to the metal shanks of the screwdrivers. The purpose of the power resistor is to limit the current flow doing the discharging process and prevent the screwdriver tips from becoming welded to the capacitor terminals.


Pull the refrigerator away from the wall. Unplug the power cord from the wall receptacle. Locate the motor starting capacitor. These capacitors are black in color, tubular in shape and have two terminals on one end. Discharge this capacitor by touching the blades of your home-made discharging tool to the terminals of the capacitor. Hold them against the terminals for a couple of minutes to make sure the capacitor is completely discharged. To verify that the capacitor is discharged simply short out the two terminals with the metal shank of one of the screwdrivers. No spark, the capacitor is completely discharged. This is very important because a good start capacitor can hold its full charge for weeks, even months after the refrigerator has been unplugged from the wall receptacle.


Remove the metal cover from the start relay box. This box can be identified by the thick red, blue and brown wires entering the box. The cover may be secured in place by a spring clip or a screw. With the cover off, pull the relay free of the compressor wingding's terminals.


Take a digital picture or make a sketch of how the wires are connected to the relay switch. Pull the female wire connectors from the male side terminals on the start relay. Some of these connectors become quite tight with age, and you may need to use long-nosed pliers to pull them free. Grasp the connectors with the pliers; do not pull on the wires.


Set the function switch on your multimeter to the X1 Ohms range. Turn the relay upside down and touch the meter probes to the “S" and “M” terminals on the relay. The meter's LCD will display “0.000” for a good relay. Turn the relay right side up and repeat this test. The LCD should now display “O.L.” for a good relay.


Turn the relay upside down again. Touch the meter probes to the “S” and “L” terminals. The LCD should display “0.000.” turn the relay right-side up and the meter should display “O.L.”


Turn the relay upside down for a third time. Connect the meter probes to the “L” and “M” terminals. The LCD should display “0.000” for s good relay. Turn the relay right-side up and the reading should still be “0.000.” A relay switch that fails any of these tests is defective and needs to be replaced.

Things You Will Need

  • 20,000 Ohm, 2-Watt, wire-wound power resistor

  • 2 jumper wires equipped with alligator clips

  • 2 flat-head, insulated screwdrivers

  • Long-nose pliers

  • Digital multimeter


  • There are two types of relays, electromechanical and solid state. This article pertains to the electromechanical, the one with the exposed coil. A solid state relay can also be tested with a digital multimeter but the testing procedure is beyond the scope of this article.