Defrost Timer

Basics of How a Defrost Timer WorksThe 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 12 - 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 6 - 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 TimerYou 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.

What's In the Box

Defrost timer