How to Test an LG Refrigerator Linear Compressor

This diagnostic confirms whether the compressor and overload are working before you pay for service. The Linear Compressor carries a 10-year manufacturer warranty, so proving a compressor failure lets you pursue warranty repair even after the general product warranty has lapsed.

Tools, Parts, and Safety First#

• 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 ~varies by model and area 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 from the wall to reach the rear. The Linear Compressor sits at the bottom rear behind a metal or cardboard cover panel. Remove the cover screws (usually 4-6 Phillips) and set it aside, exposing the black cylindrical compressor body, the overload protector and start relay, the copper refrigerant lines, and the condenser coil or fan.

Step 2 — Identify the components#

The Linear Compressor has 3 terminal pins on a block on the side of the housing. The overload protector clips over these terminals with a wire harness running to the start relay and then the main control board. On most LG models the overload and start relay are one combined assembly (LG part 6748C-0004D or similar) that slides or clips onto the terminal block. Photograph the wiring before you remove anything.

Step 3 — Remove the overload/relay assembly#

Pull the assembly straight off the compressor terminals — it is a friction fit on the pins, though some models add a retaining clip to release first — and disconnect the harness connector feeding power from the control board. Set it aside for separate testing, which leaves the three compressor pins exposed.

Step 4 — Test the compressor windings#

Set the meter to its lowest ohms range. The three terminals are labeled S (Start), R (Run), and C (Common). Measure across each pair: expect about 3-8 ohms S to C, 3-8 ohms R to C, and 6-16 ohms S to R (S-R should roughly equal S-C plus R-C). Any pair reading OL (open) means a broken winding; any pair reading 0 or near-0 means a short. Either confirms compressor failure. The internal check is the S-R relationship: because the start and run windings are wired in series through the common terminal, the S-R reading should come out close to the S-C and R-C readings added together, and a large mismatch there points to a partially failed winding even when no single pair reads fully open. Take each reading twice and let the meter settle, since a compressor that has just been running stays warm and reads slightly higher than a cold one; the point is not the exact decimal but whether all three pairs are in the expected low-ohm range and none is open or shorted.

Step 5 — Test for a ground fault#

Still on ohms, touch one probe to any compressor terminal and the other to the bare metal housing (scrape paint for good contact). It should read OL — no path from windings to housing. Any resistance between a terminal and the housing is a ground fault, a confirmed failure that must be replaced. This test is critical for safety, since a grounded compressor can energize the chassis.

Step 6 — Test the overload protector#

The overload is a thermal device that opens when temperature or current exceeds its rating. Set the meter to continuity or low resistance and probe its two terminal contacts: at room temperature you should read continuity (near 0 ohms or a beep). If it reads OL at room temperature, it has failed open and is cutting power to the compressor even though the compressor may be fine — a common, inexpensive failure. Replace the overload/relay assembly 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 read low resistance (a few ohms) between its terminals, and OL means it has failed and the compressor cannot start even with good windings. On LG models with the combined overload/relay unit, replace the whole assembly if either part tests bad.

Step 8 — Run ThinQ Smart Diagnosis and interpret#

Push the overload assembly firmly back onto the terminals, restore the harness, refit the rear cover, push the fridge back, and plug in. Open the LG ThinQ app and run Smart Diagnosis; it reports compressor status, compartment temperatures, defrost status, and fan operation. If the compressor tested good on your meter but Smart Diagnosis reports a compressor error, the control board may not be sending the start signal — a board issue rather than a compressor failure, potentially saving you an unnecessary sealed-system claim. This is the payoff of testing before you call: a service dispatch that assumes "no cooling equals dead compressor" can turn into an expensive sealed-system repair, when your own readings may show the compressor windings are healthy and only a fifteen-dollar overload has tripped. Keep your resistance numbers and the ground-fault result written down, because handing those to the technician who arrives shortens the visit and, on a warranty claim, gives LG's authorized provider a documented starting point rather than a fresh diagnosis from zero.

Troubleshooting Common Issues#

• Windings normal but overload open at room temperature: replace the overload/relay assembly — the most commonly misdiagnosed LG failure, where the compressor is fine but cannot start because the overload has permanently tripped.
• Open on one winding pair: the Linear Compressor motor winding has failed, which is covered under LG's 10-year sealed-system warranty for parts — contact LG authorized service with your model and serial number.
• Any resistance to the housing on the ground test: do not operate the unit — a grounded compressor is a hazard. Unplug it and schedule warranty service.
• All electrical tests pass but the compressor clicks once and stops: the compressor may be mechanically seized (Linear Compressors can seize if the refrigerant charge, which lubricates internally, is lost), a sealed-system failure under the 10-year warranty.
• Compressor runs but the fridge does not cool: the problem is probably not the compressor — check the evaporator fan, condenser fan, sealed system for a refrigerant leak (oil stains on tubing), or the defrost system. A compressor that runs steadily but leaves the box warm is telling you the cold is being made and simply not moved or distributed, so the fault lies downstream of the compressor you just cleared.

When Should You Call a Professional?#

EasyBear technicians serving Sacramento and the Bay Area carry LG-specific diagnostic tools and replacement parts on every service call. All sealed-system repairs (compressor replacement, refrigerant recharge, line repair) require EPA Section 608 certification, so never open refrigerant lines or replace a compressor yourself. If your compressor tests bad within the 10-year warranty, LG requires an authorized provider to perform the repair, and your diagnostic readings help the technician confirm and expedite the claim. Call too if the board is not sending a start signal despite a good compressor, if the compressor short-cycles (starts, runs a few seconds, then the overload trips it off repeatedly — a refrigerant-charge issue), or if clogged condenser coils are overheating the compressor.

Need Professional Help?#

• refrigerator repair service
• LG appliance repair
• refrigerator repair cost guide

Need help with this repair? Schedule a free diagnostic — same-day LG refrigerator service across the Bay Area.