Brand: LG
Model Number: LMXS28626S/00
Main Symptom: Fresh Food Cooling Failure
What happens & when:
1. Initial Service Visit & Diagnostic Background
Initial Symptom: Neither the fresh food section nor the freezer was cooling.
First Technician Visit: Diagnostic tech inspected the unit and identified a failed heat sheath / defrost heating element, quoting ~$900 for the repair.
Immediate Result: Replaced the heat sheath element independently. This immediately restored the freezer compartment, which cooled down and is now maintaining a steady 0°F.
2. Current Operational Status
Freezer Compartment: Fully operational, maintaining target 0°F consistently.
Fresh Food / Refrigerator Compartment: Failing to cool; maintaining ambient temperatures between 70°F and 75°F.
3. Comprehensive Diagnostics & Parts Replaced
The following diagnostic tests, component replacements, and complete teardowns have been performed to isolate the failure:
1. Defrost Heat Sheath / Heating Element:
Replaced the failed heat sheath assembly, successfully restoring full freezer cooling to 0°F.
2. French Door Air Flapper / Mullion Seal:
Replaced the vertical door flapper/gasket assembly to verify a complete thermal seal along the center door seam.
3. Multi-Air Flow Assembly / Rear Duct Manifold:
Replaced the complete rear duct manifold assembly (LG Part #ADJ74812544), which houses the integrated damper motor, thermistors, and air distribution vents.
4. Door Sensors & Switches:
Inspected and bench-tested all door open/close reed switches to confirm the control board correctly registers door closures and sends activation signals to the interior fans and dampers.
5. Main PCB Diagnostics & Forced Test Mode:
Ran manual diagnostics directly via the test switch on the main PCB/switchboard.
Cycled through test modes: verified all fans, dampers, and air vents actuate, proving there are no electrical control faults, broken fan motors, or physical air vent blockages.
6. Airflow Teardown Test (Manifold Bypass):
Removed the rear manifold panel to inspect direct evaporator performance. Frost/cooling occurs only around the immediate freezer evaporator, but cold air is not circulating up to the fresh food section under normal operational load.
4. Diagnostic Conclusion for Service Technician
Because the defrost heater, air duct manifold, damper assembly, thermistors, door flapper, and control logic have all been replaced and functional testing via the main control board switch confirms all fans and vents operate correctly, the failure is isolated to the sealed refrigerant system / linear compressor pumping loss. The compressor operates at degraded efficiency—generating just enough pressure to cool the immediate freezer evaporator to 0°F, but lacking the BTU capacity to cool the fresh food compartment.