How to Test the LG Linear Compressor and Overload Protector

LG's Linear Compressor uses a fundamentally different mechanism than traditional rotary compressors found in other brands. Instead of a rotating motor driving a crankshaft, the Linear Compressor uses an electromagnetic linear motor that drives the piston directly in a back-and-forth motion. This design produces the characteristic knocking or clicking sound that is normal for LG refrigerators but concerns many owners unfamiliar with the technology. The overload protection device on LG Linear Compressors monitors current draw and temperature, cutting power to the compressor if either exceeds safe limits.

This diagnostic guide helps you determine whether your LG refrigerator's compressor and overload protector are functioning correctly before scheduling professional service. The Linear Compressor carries a 10-year manufacturer warranty, so confirming a compressor failure allows you to pursue warranty repair even if the general product warranty has expired.

Before You Start

• Tools needed: Digital multimeter, Phillips #2 screwdriver, 3/16-inch flat-head screwdriver, flashlight, needle-nose pliers
• Parts needed: None for diagnostic testing (replacement overload ~$15-$30 if failed)
• Time required: 30-45 minutes
• Difficulty: Intermediate (requires multimeter use and working near electrical connections)
• Safety warning: UNPLUG the refrigerator and wait at least 5 minutes before accessing compressor components. The compressor and surrounding area can be hot during operation. Capacitors in the start circuit can hold charge. Never touch compressor terminals while plugged in. If you are uncomfortable working with electrical diagnostics, skip to the professional service section below.

Step-by-Step Instructions

Step 1: Access the Compressor Compartment

Pull the refrigerator away from the wall to access the rear. The Linear Compressor is located at the bottom rear of the unit, typically behind a metal or cardboard cover panel. Remove the cover panel screws (usually 4-6 Phillips screws) and set the panel aside. You will see the black cylindrical compressor body, the attached overload protector and start relay, copper refrigerant lines, and the condenser coil or condenser fan depending on the model design.

Step 2: Identify the Compressor Components

The LG Linear Compressor has 3 terminal pins on a terminal block located on the side of the compressor housing. The overload protector clips over these terminals and has a wire harness connecting it to the start relay and then to the main control board. On most LG models, the overload and start relay are combined into a single assembly (LG part number 6748C-0004D or similar). The assembly slides or clips onto the compressor terminal block. Photograph the wiring configuration before removing anything.

Step 3: Remove the Overload/Start Relay Assembly

Gently pull the overload/relay assembly straight off the compressor terminals. It is held in place by friction fit on the terminal pins. Some models have a retaining clip that must be released first. Disconnect the wire harness connector that feeds power from the control board. Set the assembly aside for separate testing. You now have direct access to the three compressor terminal pins.

Step 4: Test Compressor Windings with Multimeter

Set your multimeter to the lowest resistance (ohms) range. LG Linear Compressors have three terminals typically labeled S (Start), R (Run), and C (Common). Measure resistance between each pair of terminals. Expected readings for LG Linear Compressors: S to R should equal approximately the sum of S-to-C plus R-to-C readings. Typical values are 3-8 ohms between S and C, 3-8 ohms between R and C, and 6-16 ohms between S and R. If any reading shows OL (open line/infinite resistance), the compressor winding is broken. If any reading shows 0 or near-0 ohms, a short circuit exists. Either condition confirms compressor failure.

Step 5: Test for Ground Fault

With the multimeter still on resistance, touch one probe to any compressor terminal pin and the other probe to the bare metal compressor housing (scrape away paint if necessary for good contact). The reading should be OL (infinite resistance) indicating no current path from windings to the housing. Any resistance reading between a terminal and the housing indicates a ground fault in the compressor, which is a confirmed failure requiring replacement. This test is critical for safety as a grounded compressor can energize the chassis.

Step 6: Test the Overload Protector

The overload protector is a thermal device that opens (breaks the circuit) when temperature or current exceeds its rating. Set your multimeter to continuity or low resistance. Place probes on the two terminal contacts of the overload device. At room temperature, you should read continuity (near 0 ohms or a beep on continuity mode). If the overload reads OL (open) at room temperature, it has failed in the open position and is cutting power to the compressor even though the compressor itself may be fine. This is a common and inexpensive failure point. Replace the overload relay assembly (~$15-$30) before condemning the compressor.

Step 7: Test the Start Relay

If your model has a separate PTC (positive temperature coefficient) start relay, test it the same way. At room temperature, it should show low resistance (a few ohms) between its terminals. If it shows open (OL) at room temperature, the relay has failed and the compressor cannot start even though the motor windings are good. On LG models with the combined overload/relay unit, the entire assembly must be replaced if either component tests bad.

Step 8: Run ThinQ Smart Diagnosis and Interpret Results

Reconnect the overload assembly to the compressor (push onto terminals firmly), restore the wire harness, and replace the rear cover panel. Push the refrigerator back and plug it in. Open the LG ThinQ app and run Smart Diagnosis. The app will report compressor status, temperature readings from all compartments, defrost system status, and fan operation. If the compressor tests good with your multimeter but Smart Diagnosis reports a compressor error, the control board may not be sending the signal to start the compressor. This indicates a control board issue rather than a compressor failure, potentially saving you from an unnecessary sealed system repair claim.

Troubleshooting Common Issues

Based on your test results, here is what different findings indicate:

• If compressor windings test normal but the overload is open at room temperature, replace the overload/relay assembly. This is the most common misdiagnosed failure on LG refrigerators. The compressor is fine but cannot start because the overload has permanently tripped. Cost is $15-$30 for the part versus $800+ for compressor replacement
• If compressor windings show open on one pair of terminals, the Linear Compressor motor winding has failed. This is covered under LG's 10-year sealed system warranty for parts (labor coverage varies). Contact LG authorized service with your model and serial number
• If the compressor ground fault test shows any resistance to the housing, do not attempt to operate the unit. A grounded compressor is a safety hazard. Unplug immediately and schedule warranty service
• If all electrical tests pass but the compressor clicks once and stops, the compressor may be mechanically seized. LG Linear Compressors can seize if refrigerant charge is lost (the refrigerant provides internal lubrication). This is a sealed system failure covered by the 10-year warranty
• If the compressor runs but the refrigerator does not cool, the problem is likely not the compressor. Check the evaporator fan, condenser fan, sealed system for refrigerant leak (oil stains on tubing), or the defrost system. The compressor running without cooling suggests either fan failure preventing air distribution or loss of refrigerant charge

When to Call a Professional

Compressor testing provides diagnostic information, but actual compressor or sealed system repairs must be performed by professionals:

• All sealed system repairs (compressor replacement, refrigerant recharge, line repair) require EPA Section 608 certification. Never attempt to open refrigerant lines or replace a compressor yourself
• If your compressor tests bad and is within the 10-year warranty period, LG requires an authorized service provider to perform the warranty repair. Having your diagnostic test results (resistance readings, ground fault test) helps the technician confirm and expedite the warranty claim
• If the control board is not sending start signal to the compressor despite the compressor testing good electrically, board-level diagnosis requires specialized equipment and firmware knowledge
• If you hear the compressor start and run for a few seconds before the overload trips it off repeatedly (short cycling), a refrigerant charge issue exists. The compressor is trying to operate but encountering abnormal back-pressure from a restriction or overcharge. This requires professional sealed system diagnosis
• If the condenser coils are heavily clogged and the compressor is overheating as a result, cleaning the condenser may resolve the overload tripping. However, if the overload has already been permanently damaged by thermal cycling, both cleaning and overload replacement are needed

Cost Comparison: DIY vs Professional

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FAQ

Q: Is the clicking/knocking sound from my LG refrigerator normal? A: Yes. LG Linear Compressors produce a rhythmic clicking or knocking sound that differs from the smooth hum of traditional rotary compressors. The sound comes from the linear piston reciprocating inside the compressor. It should be steady and regular when running. Irregular, loud banging, or metallic grinding is not normal and indicates internal mechanical failure.

Q: Does the LG 10-year compressor warranty cover labor? A: LG's 10-year sealed system warranty covers parts (compressor, evaporator, condenser, tubing, refrigerant) for 10 years from purchase date. Labor coverage varies by when the unit was purchased and your location. Some models include 5 years of labor coverage. Contact LG with your serial number to confirm your specific coverage.

Q: Can I replace just the overload protector without calling a technician? A: Yes. The overload/start relay assembly is a user-replaceable part that does not involve the sealed refrigerant system. It pulls off the compressor terminals and the replacement pushes on. No brazing, refrigerant handling, or special certification required. This is the most cost-effective repair when the overload has failed but the compressor is good.

Q: How long should an LG Linear Compressor last? A: LG rates their Linear Compressors for at least 20 years of service life, backed by the 10-year parts warranty. The linear design has fewer moving parts than rotary compressors (no crankshaft, no connecting rod, no wrist pin), reducing mechanical wear. Most failures within the warranty period are related to the overload protector or control board rather than the compressor motor itself.

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