A common refrigerator problem on Samsung and LG models looks like this:
- The freezer continues cooling normally.
- The fresh-food compartment gradually becomes warmer.
- Airflow from the rear panel becomes weak.
- Heavy frost or solid ice is visible through the vent openings.
- Water runs down the rear panel.
- Water or ice collects at the bottom of the refrigerator compartment.
In my experience, this happens most often in French-door refrigerators with a bottom freezer and separate cooling systems: two evaporators and two defrost systems.
Samsung refrigerators and LG refrigerators are especially prone to this failure.
Because the freezer and fresh-food compartments have separate evaporators, one compartment can continue working while the other evaporator becomes buried in ice.
The failure may be in the defrost heater, thermal fuse, temperature limiter, wiring, or connectors. But when the complete defrost circuit tests correctly and the main control board does not supply power during a defrost command, the problem is often one or more power relays on the board.
That specific failure — and the option to replace the relays instead of the entire control board — is the focus of this article.
Safety note: This diagnosis requires testing a live appliance at approximately 120 VAC. It is not a do-it-yourself repair procedure.
Why We Do Not Remove a Frozen Evaporator Cover First
When the fresh-food evaporator is heavily frozen, the rear cover may be locked in place by ice.
Removing it in that condition is difficult and can damage the fan, temperature sensors, wiring, plastic panel, or other important components.
More importantly, removing it is usually unnecessary during the first stage of diagnosis.
The complete electrical defrost circuit can be tested from the main control board. Depending on the model, that circuit includes:
- The defrost heater
- The thermal fuse
- The temperature limiter or bi-metal thermostat
- The wiring
- The connectors
- The internal connections behind the evaporator cover
Testing from the board first shows whether the failure is in the defrost circuit near the evaporator or in the control board itself.
Testing the Complete Defrost Circuit
The circuit is tested at the appropriate main-board connector pins.
This checks the complete path from the board, through the heater and protective devices, and back to the board.
There are two basic results.
The Defrost Circuit Is Open
If the circuit has no continuity, the failure may be in:
- The defrost heater
- The thermal fuse
- The bi-metal thermostat
- The temperature limiter
- The wiring
- A connector
- An internal connection behind the evaporator cover
If the control board supplies the required 120 VAC during the defrost command, the board does not need to be replaced.
The failure is downstream from the board.
The refrigerator must then be defrosted, the evaporator cover removed, and the individual defrost components tested. The failed component or connection must be repaired or replaced.
The Defrost Circuit Tests Good
If the circuit shows the correct continuity and resistance, the heater, protective devices, wiring, connectors, and series connections are electrically intact.
This is a direct series circuit containing electrical loads and protective devices. There are no hidden electronic modules, capacitors, or switching components that would make the continuity and resistance results misleading.
The next step is to activate defrost through the service mode for that specific refrigerator and test the control-board output.
If the defrost command is active but approximately 120 VAC is not present at the correct output pins, the failure is in the main control board — usually one or more power relays.
That is how a failed relay is confirmed by testing rather than guessed from the frost pattern.
Starting Defrost Test Mode on Samsung and LG Refrigerators
Service procedures vary by brand, model, and board revision.
On Samsung refrigerators, the available commands may include:
- Force Defrost
- Fd
- rd
- A separate fresh-food defrost or relay test
On many LG refrigerators, service mode is activated with a test button located directly on the main control board.
The button is often pressed three times, after which the display may show a code such as 33 33.
That procedure is common, but it is not universal. The number of button presses, display code, and test sequence can vary by model, production year, and board version.
The diagnostic principle remains the same:
- Test the complete defrost circuit.
- Activate the correct service mode.
- Check for approximately 120 VAC at the board output.
- Confirm that the heater energizes.
When the heater operates, the ice begins to melt. Water may drip onto the warm element and produce a noticeable hissing sound.
Two Control-Board Repair Options
Once a failed relay has been confirmed, the customer can choose between two legitimate repair options.
Option 1: Replace the Complete Control Board
A new main control board commonly costs $300 or more, before shipping and sales tax.
Some customers prefer a completely new board because they believe it may improve the refrigerator’s overall reliability.
I cannot honestly say that a new board will always make the refrigerator more reliable. It is simply one reasonable repair option, and the final choice belongs to the customer.
Option 2: Replace the Failed Relay
If testing confirms that one or more power relays have failed, those relays can be replaced individually.
A relay usually costs no more than $12.50. Diagnosis, board removal, soldering, reinstallation, and final testing are billed separately.
Relay replacement is a dependable component-level repair when the failed output has been identified correctly.
It avoids the cost of an entire control board and can reduce delays caused by ordering and waiting for the complete electronic assembly.
The savings compared with complete board replacement may be approximately $250–300.
Testing After Relay Replacement
After the relay repair, the control board is reinstalled and service mode is activated again.
We verify:
- Approximately 120 VAC is present at the board output.
- The defrost heater energizes.
- The evaporator temperature begins to rise.
- The ice begins to melt.
- The defrost system completes its operation.
Dripping water and a light hissing sound are often noticeable after the heater begins warming.
This confirms that the control board is once again supplying power to the defrost circuit.
When the Evaporator Cover Must Be Replaced
The evaporator cover does not automatically require replacement every time the evaporator freezes.
Its condition must be evaluated separately.
Signs of a damaged cover include:
- A large mass of ice visible through the vents
- Water and condensation covering the plastic
- Water running down the panel
- Water or ice collecting at the bottom of the fresh-food compartment
- A visibly distorted panel
- The fan contacting ice
Samsung and LG explain that prolonged icing can saturate the foam insulation inside the cover, preventing it from insulating correctly.
I agree with that assessment.
When the cover has remained surrounded by ice and water, the foam can become saturated or physically damaged.
I have inspected enough of these covers that their condition is often obvious from the outside. If the panel can be removed and inspected internally, even better.
When the water, ice, and distortion show that the insulation is no longer serviceable, the cover should be replaced.
A repaired control board will not restore damaged insulation. A new evaporator cover will not repair a failed board relay. They are separate parts of the same repair.
Real LG Repair: Two Failures and Two Visits
In one LG refrigerator repair, the fresh-food compartment stopped cooling because the evaporator was completely frozen.
The refrigerator was relatively new — approximately one to one and a half years old.
Testing from the main control board showed an open defrost circuit.
After the refrigerator was defrosted, the failed protective assembly was found: the thermal fuse and temperature limiter.
The assembly was replaced, the heater was tested, and the defrost circuit began operating again.
Approximately 15–16 days later, the problem returned.
During the second visit, the circuit was tested again. Using the board-output method described above, two failed relays on the main control board were identified.
The refrigerator had developed two separate failures:
- Failed defrost components near the evaporator
- Two failed power relays on the main control board
Instead of purchasing a complete $300–350 control board, the two failed relays were replaced.
After the repair:
- The board supplied power again.
- The heater energized.
- The defrost system operated normally.
- Cooling returned to the fresh-food compartment.
The evaporator cover did not require replacement. The refrigerator was still fairly new, and the panel had not suffered serious damage from long-term icing.
Real Samsung Repair: Good Circuit but No 120 VAC Output
In another repair, the Samsung fresh-food compartment became warm while the rear evaporator cover was completely frozen.
Water was running down the panel, condensation was visible outside the cover, and airflow had nearly disappeared.
Testing from the main control board confirmed that the complete defrost circuit was electrically intact.
The service mode specified for that model was then activated.
Approximately 120 VAC did not appear at the control-board output.
That confirmed a failed power relay.
After the relay was replaced and the test was repeated:
- Voltage appeared at the board output.
- The defrost heater energized.
- The ice began melting.
- Water started dripping.
- The characteristic hissing sound became audible.
The evaporator cover also had to be replaced. It had remained frozen long enough to become waterlogged, and its insulation was no longer serviceable.
This Article Does Not Cover Every Cause of Evaporator Frost
A good question is: how can the evaporator still freeze if the defrost system is operating?
That can absolutely happen.
This article focuses specifically on main control-board failures and replacement of the board’s power relays.
Briefly, an automatic defrost cycle is limited by both time and temperature. Under some conditions, one or both limits may be insufficient to remove all accumulated ice.
Localized frost can also develop because of:
- A failed evaporator fan motor
- A low refrigerant charge
- Uneven airflow
- Sensor problems
- A restricted drain
- Other cooling-system conditions
Those failures require a separate diagnostic discussion.
Frequently Asked Questions
Why does the freezer work while the refrigerator section becomes warm?
Refrigerators with two evaporators have separate cooling and defrost systems for the freezer and fresh-food compartments.
If the freezer system is operating correctly, the freezer continues cooling normally. If the fresh-food evaporator freezes over, that compartment must be diagnosed separately.
Can I simply defrost the refrigerator?
Yes.
Without automatic defrost, the refrigerator becomes similar to an older model that had to be manually defrosted — the kind many of our grandparents used.
It is inconvenient, but the refrigerator can continue working. Once the ice melts, cooling and airflow return. The evaporator will eventually freeze again, and another manual defrost will be required.
What does an open defrost circuit mean?
If the control board supplies 120 VAC but the defrost circuit is open, the board does not need replacement.
The refrigerator must be defrosted so the evaporator area can be accessed. The failed heater, thermal fuse, bi-metal thermostat, temperature limiter, wiring, connector, or internal connection must then be identified and repaired.
Can the refrigerator be tested without pulling it out?
Probably not.
The main control board is usually located behind or on top of the refrigerator. Proper access is needed to reach the connectors and safely test the live output voltage.
If the refrigerator is heavy, built into cabinetry, or trapped by flooring, it will most likely still need to be pulled out.
If the defrost system works, why does the evaporator still freeze?
That is an excellent question.
An evaporator can still freeze even when the defrost system operates. The cycle is limited by time and temperature, and those limits may not always be enough to remove all accumulated ice.
Localized icing can also result from a failed evaporator fan, low refrigerant charge, uneven airflow, sensor problems, or a restricted drain.
This article focuses specifically on control-board relay failures. The other causes require a separate diagnostic discussion.
Should I turn off and defrost the refrigerator before the technician arrives?
If you plan to schedule service, do not turn off or defrost the refrigerator beforehand.
An experienced technician can learn a great deal from the frost pattern:
- Whether the buildup is soft frost or solid ice
- Whether it begins at the top or bottom
- Whether the evaporator is fully or partially covered
- Whether the drain pan contains water or ice
After a complete defrost, these and other important diagnostic clues disappear.
Does the complete control board always need replacement?
No.
The customer may choose a new control board or component-level replacement of the confirmed failed relays.
A relay usually costs no more than $12.50. Labor is billed separately, but the savings compared with complete board replacement may be approximately $250–300.
When should the evaporator cover be replaced?
The cover should be replaced when it is distorted, waterlogged, surrounded by heavy ice, leaking water down the panel, or allowing water to collect at the bottom of the fresh-food compartment.
Those conditions indicate that the internal foam insulation is no longer serviceable.
Final Takeaway
The goal is to determine where the defrost system stopped working.
If the circuit is open, the failure is near the evaporator or in the wiring.
If the complete circuit tests correctly but the main control board does not supply approximately 120 VAC during service mode, one or more power relays have failed.
The customer can then choose between complete control-board replacement and component-level relay repair.
Replacing the confirmed failed relay can restore the defrost system without purchasing an unnecessary complete control board.
More real appliance repair cases with photos and confirmed diagnoses are available in the EasyFix repair blog.
The EasyFix team 🤝 No Upsells. No Nonsense. Just Honest Work.
📍 Serving Clark & Cowlitz Counties and the Portland Metro Area
