Before you decide to replace your defrost timer, it’s a good idea to troubleshoot the timer to make sure it is, in fact, the problem. Before you can test the timer, you’ll need to know how the defrost timer works.
The circuitry of a refrigerator defrost timer is surprisingly simple. Follow the below advice to test your defrost timer.
How do I know the defrost timer needs to be replaced?
There’s really no way to know if your defrost timer needs to be replaced without testing the simple circuitry. However, if your refrigerator is having any of these symptoms, then replacing the defrost timer could solve your refrigerator problems.
1) Refrigerator is too warm
2) Freezer won’t defrost
3) Freezer is too warm
4) Frost builds up on the freezer coils
Basics of How a Defrost Timer Works
The defrost timer has four pins labeled from 1 to 4. Each pin has its own function in the operation of the timer.
Pin 1: The main input power is attached to pin 1.
Pin 2: When in defrost mode, the power (pin 1) connects to pin 2, which activates the defrost mode. Most defrost timers stay in defrost mode for 30 minutes.
Pin 3: This is your ground / neutral wire. It will be separated from the other three pins.
Pin 4: When the timer is not in defrost mode, the power (pin 1) connects to pin 4, which activates the compressor and fan. Most timers stay in this mode for 10 hours.
To test if the defrost mode is working, apply voltage to pin 1. When the power supply is turned on, you should be able to measure the voltage on pin 2.
Once the timer advances past 30 minutes, the compressor and fan should turn on. You will know that the defrost timer is working if you measure voltage on pin 4 when the timer is not in defrost mode.
The compressor and fan pin should be active for 10 hours (or however long your defrost timer is designed to run). Once the 10 hours is over, the defrost timer will switch back to pin 2, activating the defrost.
Test the Defrost Timer
You can test a defrost timer by measuring the resistance in the circuits when the timer is in each mode.
When the defrost timer is in defrost mode, you should measure an open circuit between pin 1 (main power input) and pin 4.
When the defrost time has advanced past defrost mode, you should measure and open circuit between pin 1 (main power input) and pin 2.
You’ll also want to verify that the motor is working. You can do this by applying power to the timer while the timer is in defrost mode. You want to make sure the motor advances the timer. See the below video for more details.