LG LFX31945ST Service Manual

The LG LFX31945ST is a French Door Refrigerator featuring a 31 cubic foot capacity, InstaView Door-in-Door, Linear Cooling, SmartThinQ technology, Craft Ice maker, and Door Cooling+. This service manual provides detailed technical information for qualified service technicians, including safety precautions, product specifications, disassembly/assembly instructions, component testing, error codes, and wiring diagrams.

1. Safety Precautions & Warnings 2. Product Specifications 3. Model Identification & Parts 4. Disassembly & Assembly Procedures 5. Component Testing & Diagnostics 6. Error Code List & Troubleshooting 7. Wiring Diagrams & Schematics 8. PCB Layouts & Connector Details 9. Refrigerant System Information 10. Software Update Procedures 11. Exploded Views & Parts List

Safety Precautions & Warnings

This section outlines critical safety information for service personnel to prevent injury, electric shock, or product damage.

Hazard Type	Precaution
Electrical Shock	Always disconnect power before servicing. Verify capacitor discharge.
Refrigerant	Use proper recovery equipment. Avoid open flames. Wear protective gear.
Sharp Edges	Wear cut-resistant gloves when handling panels, evaporator, or condenser.
Heavy Parts	Use two people or proper lifting equipment for doors and compressor.
Electrostatic Discharge (ESD)	Use grounded wrist strap when handling PCBs.

WARNING! This manual is for trained technicians only. Incorrect repair can create safety hazards.

Product Specifications

Model: LFX31945ST
Type: French Door Refrigerator with Bottom Freezer
Total Capacity: 31.0 cu. ft. (878 liters)
Refrigerant: R-600a (Isobutane)
Electrical: 115 VAC, 60 Hz, 7.5 A
Dimensions (HxWxD): 69.875" x 35.75" x 34.75"
Door Swing: Reversible (Right/Left Hand)
Key Features: InstaView, Linear Compressor, SmartThinQ, Craft Ice, Door Cooling+
Weight: 326 lbs (148 kg)

Model Identification & Parts

Locate the model and serial number on the interior wall of the refrigerator compartment. Use these numbers when ordering parts.

Main Control Board (PCB): Part # 6321ER1002A
Linear Compressor Assembly: Part # 6751ER1003J
InstaView Door Assembly: Part # MCA73875501
Craft Ice Maker: Part # 6755ER4001B
Evaporator Fan Motor: Part # 4681ER2002D
Condenser Fan Motor: Part # 4681ER1003A
Temperature Sensors (Various): See parts list for specific codes.

Note: Always verify part compatibility using the full model number.

Disassembly & Assembly Procedures

Step-by-step instructions for accessing internal components.

Door Panel Removal: Remove hinge cover, disconnect wiring harness, support door, remove hinge bolts.
Main Control Board Access: Remove top grille, disconnect power, remove mounting screws, disconnect connectors.
Evaporator Cover Removal: Remove rear panel in freezer compartment, detach defrost heater and sensor connectors.
Craft Ice Maker Removal: Open freezer drawer, remove ice bucket, disconnect water line and electrical connector, remove mounting screws.
Compressor Access: Remove rear service panel, recover refrigerant (qualified personnel only), disconnect electrical and tubing.

CAUTION! Take photos or notes of wire routing and connector positions before disassembly.

Component Testing & Diagnostics

Use a multimeter to test components. Refer to resistance and voltage values in the table below.

Component	Test Procedure	Expected Value
Linear Compressor	Measure resistance between terminals (P-C, P-A, C-A).	See specific compressor datasheet (typically 5-20 Ω).
Defrost Heater	Measure resistance across heater terminals.	20 - 40 Ω (approx.)
Evaporator Fan Motor	Check for 120VAC at connector. Measure coil resistance.	Continuity present. Voltage present when calling for cooling.
Temperature Sensor (Thermistor)	Measure resistance at room temp (approx. 77°F/25°C).	~10 kΩ (varies with model, check chart).
Door Switch	Check continuity. Open circuit when door closed, closed when open.	Continuity changes state with door position.

Error Code List & Troubleshooting

The main PCB displays error codes via the control panel or LED blink patterns.

Error Code	Description	Possible Cause	Action
FF / 88	Communication Error (PCB to Display)	Loose harness, faulty display or main PCB.	Check connectors J3, J4. Replace display or main PCB.
PF	Power Failure	Power interruption. Normal after outage.	Reset unit. Check household power.
dH / dF	Defrost Heater Error	Open heater, faulty defrost sensor, or relay.	Test heater resistance. Check defrost thermistor.
CE / LE	Compressor Error / Linear Inverter Error	Compressor malfunction, inverter PCB fault, wiring.	Check compressor windings, inverter PCB connections.
IE / ICE	Ice Maker Communication Error	Faulty ice maker assembly or connection.	Check harness to ice maker. Replace ice maker assembly.

Wiring Diagrams & Schematics

Refer to separate fold-out pages or PDF files for full-size wiring diagrams (W-1, W-2). Key connections:

Main Power Input: L1 (Black), N (White), G (Green/Yellow) to main PCB.
Compressor Circuit: From inverter PCB to linear compressor terminals.
Fan Circuits: Evaporator fan (FF), condenser fan (CF) connections to main PCB.
Sensor Network: Multiple thermistors (Fresh Food, Freezer, Defrost, etc.) connected to analog inputs on main PCB.
Door & Display: Harness from control panel to main PCB (J3, J4).

Tip: Use highlighter to trace the specific circuit you are diagnosing.

PCB Layouts & Connector Details

Main PCB (Part # 6321ER1002A) connector pin-out summary.

Connector	Pin	Function	Signal
J1 (Power)	1	Line (L)	120VAC
	2	Neutral (N)
	3	Ground (G)
J5 (Compressor Inverter)	1	Drive Signal	PWM
J5 (Compressor Inverter)	2, 3	Feedback
J7 (Evap Fan)	1, 2	Fan Motor Power	+12VDC
CN701 (Sensors)	Multiple	Thermistor Inputs	0-5VDC

Refrigerant System Information

Refrigerant Type: R-600a (Isobutane) - FLAMMABLE.
Charge Amount: 2.12 oz (60 grams) ± 5%.
Oil Type: Polyolester (POE) oil.
Service Ports: Process stub on filter-drier (low side only). High side does not have a service port.
Evacuation & Charging: Must be performed by certified technician using dedicated R-600a equipment. System must be properly evacuated before charging.

WARNING! R-600a is flammable. No brazing on pressurized system. Follow EPA 608 and all local codes.

Software Update Procedures

Main PCB firmware can be updated via USB service dongle (LG SVC dongle).

Download correct firmware file (.lfr) from LG Service website for model LFX31945ST.
Copy file to root of FAT32 formatted USB drive.
With refrigerator powered on, insert USB drive into service port on main PCB.
PCB LED will blink rapidly during update. Do not power off.
Update completes when LED returns to steady state. Remove USB drive.
Perform a power cycle (unplug for 1 minute, then reconnect).

Note: Incorrect firmware can render the PCB inoperable.

Exploded Views & Parts List

Refer to diagrams (Fig. 1 through Fig. 15) for component location and assembly relationships.

Fig. 1: Cabinet Assembly & Insulation
Fig. 2: Door Assembly (Right/Left, InstaView)
Fig. 3: Refrigerator Compartment Interior (Shelves, Crispers)
Fig. 4: Freezer Compartment & Drawer Assembly
Fig. 5: Machine Compartment (Compressor, Condenser, Fans)
Fig. 6: Evaporator & Defrost System
Fig. 7: Ice Making System (Craft Ice & Main Ice Maker)
Fig. 8: Water Dispenser & Filter System
Fig. 9-15: Electrical Harness Routing, Bracket Details

Service Contact: LG Electronics Service Division: 1-800-243-0000. Website: www.lg.com/us/support.