Where is the defrost timer located in a refrigerator

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?

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.

Watch this video by YouTuber Bill Newberry for step-by-step details.

Modern, state of the art refrigerators use solid state circuitry to control the defrost cycle, but entry level refrigerators as well as older refrigerators use a timer to control the defrost system. A defrost timer is nothing more than a motor-driven clock that opens and closes internal contacts that control the electric current flowing to the hermetically sealed compressor and to the defrost heating elements.

Types of Defrost Timers

There are two types of defrost timers used in modern refrigerators -- constant, or continuous run timers, and accumulative timers. Constant or continuous run defrost timers run continuously as long as the refrigerator is plugged in. Accumulative defrost timers run only when the compressor is running. Accumulative defrost timers are also known as demand defrost.

Three Terminal Devices

Almost all defrost timers are three-terminal devices with one terminal common to both the defrost heater circuit and the hermetically sealed compressor-motor circuit. One of the other two terminals connects to the compressor-motor and the other to the heaters. The defrost timer receives power to its common terminal from the cold control.

Cam Operated Contacts

All timers, whether constant or accumulative run timers, contain two sets of normally open, cam actuated contacts. During the refrigeration part of the cycle the cam closes the first set of contacts directing the flow of electricity to the compressor-motor. During the auto defrost part of the operation cycle the rotating cam allow the first set of contacts to open, shutting down the compressor and closing the second set of contacts, sending electric current to the defrost heating elements.

Manual Operation

All defrost timers have a slot in which a screwdriver can be inserted to operate the timer manually, reports Parts Select. By turning the screwdriver in a clockwise direction you will be able to open and close the internal contacts manually. When you hear the first click, the compressor will shut down and the defrost heaters will come on. On the second click, the defrost heating elements will shut off and the compressor starts running again.

Time Intervals

Refrigerator manufacturers choose constant run defrost timers or accumulative defrost timers that operate on 6-, 12- or 24-hour intervals. A 6-hour interval timer means that the refrigerator will auto defrost once every 6 hours, a 12-hour interval timer once every 12 hours and a 24-hour interval timer once every 24 hours.

Do all fridges have a defrost timer?