Defrost Clock Wiring Diagram

[Yamila Comejo]

Acommon problem found when troubleshooting a freezer that uses an electric heater as its supplemental heat source is a frozen evaporator coil. Although there are several possible causes for this issue, one common cause is a faulty defrost timer. Either the defrost timer fails to initiate a defrost cycle or the defrost cycle is terminated too quickly.

A defrost timer initiates a defrost cycle by an internal time clock: if the timing mechanism fails, a defrost cycle will never be initiated. The defrost timer is also part of the termination controls. If the defrost timer or an associated termination control fails, the system may not stay in defrost long enough to adequately defrost the evaporator.

To test the defrost timer and its associated termination controls, manually advance the timer into defrost. Most electromechanical timers can be advanced into a defrost cycle by rotating a dial on the front of the timer. For digital timers or controllers, follow the instructions by the control manufacturer to initiate a defrost cycle.

Next, check and see if the defrost cycle has been initiated. Referencing the wiring diagram of the system or of the defrost timer, identify the defrost circuit and place an ammeter on that circuit. The ammeter should measure the amperage of the energized electric heaters. If no amperage or very small amperage value is measured, then the problem may not lie with the defrost timer but with a component of the defrost circuit, such as the electric heaters or safety switch. If a manual defrost cycle has been initiated and the system seems to be defrosting the evaporator normally, then the likely problem is the defrost timer not initiating a timed defrost.

If, when manually advancing the timer into defrost, the defrost cycle is terminated immediately or soon after the cycle is initiated, then the issue may lie with the terminating components. Most mechanical timers will have an internal solenoid that when energized, will switch the system back into its cooling cycle. This internal solenoid is energized by a temperature switch mounted on the evaporator. It is designed to close at a specific temperature (typically around 55F) to ensure the evaporator is void of ice. It is not uncommon for these temperature switches to be stuck closed and cause the defrost cycle to be terminated too quickly.

A quick test to prove this is the issue is to electrically disconnect the termination switch at the timer and again, manually advance the timer into a defrost cycle. If the system stays in defrost, then the problem lies with the temperature termination switch. Most defrost timers will have a backup time period, which will terminate the defrost cycle by time if the temperature termination switch fails to end the defrost cycle.

It is possible to leave the defrost cycle energized and verify the evaporator is defrosting normally. While monitoring the defrost cycle, time the cycle and see when it terminates. It should terminate based on its backup timer setting. This will also verify if the clock on the defrost timer is or is not working. Do not leave the system unattended during this test, just in case the defrost fails to terminate. If needed, as a temporary fix, leave the temperature switch disconnected until it can be replaced. However, do not leave it disconnected permanently and solely rely on the backup timer to terminate the defrost cycle. This can cause the evaporator to be over defrosted.

Many reach-in freezers use an electronic temperature controller, which will also control the defrost cycle of the freezer. There is no separate defrost timer. They typically control the defrost cycle in the same manner as a separate defrost timer. The cycle is initiated by time and terminated by temperature; however, instead of a temperature switch terminating the defrost cycle, it will use a temperature sensor.

The electronic controller will terminate the defrost cycle at a temperature measured by the temperature sensor attached to the evaporator coil. When these sensors fail, they can also cause the defrost cycle to terminate too quickly. These tend to be a little more difficult to troubleshoot, and it may not be possible to simply disconnect the sensor and test the cycle. Instead, it will be necessary to get into the programming menu of the controller and see the actual temperature of the sensor to verify if that is the issue. Also, some electronic controllers will have a minimum defrost cycle, which means they may not immediately terminate the defrost cycle when manually advanced but will not run long enough to adequately defrost the coil.

If the termination sensor is found to be the issue, adjust the termination value on the controller to a very high value to allow it to stay in defrost until its backup time expires. This will allow technicians to get the system running again until the sensor can be replaced. Again, remember to come back and replace the temperature sensor and not leave it terminating on a timed cycle.

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It says OEM which is Original Equipment Manufacture part, so if it really is that is a good replacement and should come with a detailed instruction sheet to compare your wiring with to know what terminal to attach the flying lead to.

Lots of times the manufactures will actually sub a new timer that has a longer duration between defrost, (the 12 hour timer is a sub for a lot of 8 and 10 hour timers as the Amazon page says. Generally a few hours longer between defrost cycles isn't going to make much difference.

As far as the length of defrost time you really want to keep that as close to the original specs as possible but the difference between replacing a 20 or 21 minute with a 30 minute timer isn't going to really be noticed. The defrost t-stat should usually shut the heater off before the full time allotted for defrost has been reached.

With a longer duration timer the temps may rise a little higher then desired after a defrost and take a little longer for the system to pull the temps back down to the set temp because you will have a longer time before the compressor comes back on to start cooling - during this lag between the defrost t-stat opening and shutting off the heater and the remaining defrost time running out on the timer the temps will be getting warmer.

The defrost timer is the unsung hero of your walk-in refrigerator, orchestrating the delicate balance between cooling and defrosting. This component ensures that your unit runs efficiently, preventing frost buildup that can insulate coils and lead to a lukewarm unit. Understanding how to wire and set up your timer is crucial for maintaining the longevity of your cooler and keeping your energy bills low.

At its core, a defrost timer functions as a clock, regulating the defrost cycle to prevent ice buildup. This section will break down the operation of a timer, explaining how it switches the system from cooling to heating to maintain efficiency.

Assembling a defrost timer is akin to piecing together a puzzle where every piece is vital. This section will guide you through the assembly process, ensuring that every component is correctly installed for optimal performance.

Regular maintenance of your timer is crucial for the smooth operation of your walk-in refrigerator. This section will offer maintenance tips to help you avoid emergency breakdowns and ensure your unit runs without a hitch.

The right defrost timer not only keeps your refrigerator running efficiently but also extends its lifespan. This section will discuss how avoiding ice buildup through proper defrost timing can save you from premature wear and tear on your refrigerator.

In an era where energy conservation is paramount, the defrost timer is a valuable ally. This section will explain how setting your defrost timer correctly can lead to reduced energy consumption and lower bills.

Common timer issues may include the timer failing to advance, getting stuck in a single mode, or not initiating the defrost cycle, which can cause a buildup of ice around the evaporator coils. This can be due to a malfunctioning valve, fan, or thermostat, or a short in the electrical circuit.

If you notice that your refrigerator is not defrosting properly, or if the compressor is not running on schedule, it might be time to rewire or replace your timer. Other signs include excessive ice formation or unusually high temperatures within the refrigerator, indicating that the cut-in and cut-out cycles are not functioning correctly.

Should the defrost sensor fail, it may cause the refrigerator to defrost too often or not enough. This can lead to either an unnecessary energy drain or a buildup of ice, which can put pressure on the condenser and reduce the efficiency of the refrigeration cycle.

A defrost timer is designed to last for years, but its longevity can be affected by the operational demands placed on it. Regular maintenance and keeping an eye on the low pressure control can help extend its life.

To defrost a commercial cooler, you can manually initiate the defrost cycle via the timer or control system. Some models have an automatic defrost function that operates based on the timer or when the evaporator temperature reaches a certain point, which makes the process easier and more efficient.

A timer controls the intervals between defrost cycles and their duration in a walk-in freezer. It temporarily shuts off the cooling to allow the heater to melt the ice, ensuring that the evaporator operates effectively and the refrigerant can migrate to the evaporator without obstruction.

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