Modern refrigerators have a defrost function with a defrost timer, thermostat, heater, and drain, combined with an evaporator fan motor. You may need to test your defrost timer at some point.
Step 1 - Understand What and Where
Like a clock, this keeps the rhythm of defrosting and cooling going according to pre-set time intervals. If it fails to make the switch-over from defrost to cooling or back again, test the defrost timer first.
The timer is commonly behind the front grill “toe-kick” at the bottom but can be elsewhere depending on the model.
Step 2 - Do a Simple Test
Mark the position of the timer’s stem with a pencil. Turn the stem with the screwdriver until it clicks so the defrost cycle begins. If the timer is working, after 10-30 minutes, the cooling mode will re-start and the stem will return to its original position.
Step 3 - Do a Complex Test
Remove the screws holding the timer in place and pull the connector plug out to disconnect the wires.
Test the common terminal or white wire by touching it with one probe of a multi-tester set to ohms (X1) and touching the other three terminals in turn with the other probe. At least two pairs of terminals should show a reading of zero indicating continuity. The third pair should show infinity or no continuity.
Turn the timer until it clicks and now the results of the above test will be reversed, if not, the timer needs replacing.
Step 4 - Buy a New Timer
There is no standard timer so order it with the make, serial, and model numbers handy. The price is usually $20 to 40.