How To Test the Defrost Heater
The defrost heater is usually located at the back of a side by side freezer or under the floor of a top freezer. It will be necessary to remove obstructions such as the contents of the freezer, freezer shelves and icemaker to get to the heater.
Before testing the defrost heater, unplug the refrigerator to avoid an electrical shock hazard.
The panel may be held in place by retainer clips or screws. Remove the screws or depress the retainer clips with a small screwdriver. On some older top freezers it is necessary to remove the plastic molding to access the freezer floor. Removal of that molding can be tricky - never force it. If you decide to remove it, you do so at your own risk - it is prone to breakage. Warm it first with a warm, wet bath towel this will make it less brittle and a little more pliable.
There are three primary types of defrost heater elements; exposed metal rod, metal rod covered with aluminum tape or a wire coil inside a glass tube. All three elements are tested in the same way.
The heater is connected by two wires. The wires are connected with slip on connectors. Firmly pull the connectors off of the terminals (do not pull on the wire). You may need to use a pair of needle-nose pliers to remove the connectors. Inspect the connectors and the terminals for corrosion. If the connectors are corroded they should be replaced.
Test the heating element for continuity using a multitester. Set the multitester to the ohms setting X1. Place a probe on each terminal. The multitester should display a reading somewhere between zero and infinity. Because of the number of different elements we cannot tell what your reading should be, but we can be certain of what it shouldn't be. If the reading is zero or infinity the heating element is definitely bad and should be replaced.
You may get a reading between those extremes and the element may still be bad, you can only be certain if you know the correct rating of your element. If you can find the schematic, you may be able to determine the proper resistance rating. Also, inspect the element as it may be labeled.