Fixing Defrost System

Isolating the Problem

Warm humid air entering the freezer section when you open the door collects on the evaporator coils as frost. In a few days this frost buildup would completely fill the evaporator section. The defrost timer periodically turns the compressor off and energizes the defrost heater. The defrost heater melts the frost and the condensate runs down into the condensate pan under the refrigerator.

Check the defrost heater first by locating the defrost timer under the refrigerator, behind the kick plate. Use a flat blade screwdriver to advance the timer knob clockwise until the compressor stops. This should energize the defrost heater for 15 to 20 minutes. Listen for hissing and popping sounds from the evaporator or condensate coming out the drain hole at the top of the refrigerator. Remove the condensate gutter off the drain hole for a better look. If the defrost heater seems to work then prepare to replace the timer. If nothing seems to be happening, unplug the refrigerator and start removing the evaporator cover from the bottom of the freezer section by removing the evaporator fan shroud and any other fittings on top of the metal cover. Remove all of the screws from the cover and lift it up at the back and pull towards the back and then pull it out. Remove the styrofoam cover and examine the defrost heater.

Do you see any evidence of the heater element burning inside the glass tube? If you can't confirm visually that the heater element has burned in two, remove the wire nuts from the wires leading away from the heater element and measure the resistance with an ohmmeter. If an open circuit is indicated, replace the defrost heater. There is a defrost thermostat in series with the defrost heater. It should be closed as long as the evaporator coil area is less than 55 deg. F. Though the thermostat rarely fails, check it if the timer and heater check out OK but the heater won't come on.

Replacing the Defrost Heater

If the defrost heater consists of two heaters in series and only one has failed, replace them both. Bend the tabs at the end of the heater brackets to remove the shield covering the old heater. Disconnect the spade terminals and lift out the old element(s). Use your refrigerator model number to buy a new heater. Don't touch the quartz glass of your new heater with your fingers - the oils and salts on your fingers will etch the glass. Handle the new heater element by the end caps and position it into the holder bracket, replace the reflector shields and slide the spade terminals back on. Replace the evaporator covers and check for proper operation.

Replacing the Defrost Timer

Part No. WR9X480

Make sure the refrigerator is unplugged. Remove the screw holding the defrost timer bracket to the lower cross bar and slide the bracket and defrost timer out far enough to remove the wire terminals off the timer. As you remove a wire from the old timer, replace it on the same terminal on the new timer. Remove the two mounting screws from the old timer and use them to install the new timer. Slide the new timer and the timer bracket back under the refrigerator and secure the bracket by replacing the mounting screw. This completes the installation of the new timer.