LG Air Conditioner Error 21
⚡ Quick Answer: The LG air conditioner error code 21 indicates a communication failure between the indoor and outdoor units, often caused by an inverter-related fault... ⚠️ Difficulty Varies
What Does Error 21 Mean?
The LG air conditioner error code 21 indicates a communication failure between the indoor and outdoor units, often caused by an inverter-related fault. This may result in the AC shutting down or failing to start, with the outdoor unit displaying a fault indicator. Common causes include compressor overcurrent, blocked airflow, and faulty electrical components. Addressing these issues promptly can help restore functionality.
Common Symptoms:
- Air conditioner shuts down or will not start when CH21 appears
- Compressor stops running or system cuts out shortly after startup
- Outdoor unit fault indicator with indoor display showing CH21
Possible Causes
- Compressor overcurrent / inverter DC peak fault (medium)
- Blocked airflow or dirty condenser/coils leading to compressor strain (medium)
- Faulty outdoor power module (IPM/PCB) or electrical faults (medium)
How to Fix Error 21
DIY Fix Perform basic checks and reset
- Power off the AC at the breaker or unplug it for 5‑10 minutes
- Ensure outdoor unit has clear airflow and no debris blocking condenser
- Clean or replace air filters
- Restart the unit and observe if CH21 persists
Technician Only Professional diagnostics and repair
- Measure compressor current draw and compare with specification
- Inspect inverter PCB/IPM and outdoor unit wiring for damage or shorts
- Check compressor windings and insulation resistance
- Assess refrigerant levels and outdoor unit thermal performance
Parts needed: inverter PCB/IPM module, compressor, wiring/connectors, capacitor (if applicable)
- CH21 persists after reset and filter/airflow checks
- Signs of electrical burning, unusual noises, or repeated tripping
Next step
Choose the next step for 21
Confirm the diagnosis before ordering. An error code can identify the system involved, but it does not prove that a specific part has failed.
Most relevant component to inspect
Compressor
Compresses refrigerant within the sealed cooling system and requires specialized service equipment.
- Typical part-only price
- $180 - $600
- DIY difficulty
- Hard
- Estimated time
- 120-240 mins
Where can I find the model number?
Check the rating label around the door, lid, frame, rear panel, or inside the appliance cabinet. Use the complete model number, including suffixes.
Verify the complete model and part number on the retailer's compatibility page before ordering.
Other parts options
Check related components first; use model search as a fallback.
Wiring Harness
Connects controls, sensors, motors, and other electrical components inside the appliance.
Capacitor
Stores electrical energy to assist in starting or running the motor efficiently.
Model-compatible Air Conditioner parts
Enter the complete model number to browse compatible replacement parts. This is a model-based parts search, not a diagnosis that a specific component failed.
Affiliate disclosure: As an Amazon Associate I earn from qualifying purchases. We may earn a commission from other qualifying purchases or service requests made through links on this page, at no additional cost to you. Recommendations are based on repair relevance, not commission rate.
Optional routine care
Maintenance supplies
These products support cleaning or routine upkeep. They are separate from the possible repair components above and are not claimed to fix this error code or symptom.
Air Conditioner Fin Cleaner
For routine cleaning of accessible coil fins when permitted by the manufacturer. Disconnect power and follow product and appliance instructions.
Model-Compatible Washable AC Filter
A reusable filter option only where the appliance supports one. Match the full model, dimensions, and filter specification.
Compatibility check required: use the complete appliance model and compare the existing filter, bag, or specification before ordering.
Affiliate disclosure: As an Amazon Associate I earn from qualifying purchases. Recommendations are based on routine-care relevance, not commission rate.
Technical Specifications
| wattage | N/A |
|---|---|
| component | Communication Cable |
| resistance | N/A |
| part_number | LG 6711A20043A |
| voltage_rating | 220V AC |
Common Questions
What does 21 error mean on lg air conditioner?
The 21 error indicates a communication failure between indoor and outdoor units, often related to inverter faults.
Can I fix lg air conditioner 21 error myself?
Yes, you can perform basic checks like resetting the unit and ensuring clear airflow.
How much does it cost to fix 21 error?
Repair costs for the 21 error typically range from $150 to $800, depending on parts and labor.
When should I call a technician for 21?
Call a technician if the error persists after resets, or if you notice electrical burning or unusual noises.
Sources & References
- LG Aircon Error Code CH 21 – How to Fix It? (community)
Data last verified: 2026-07-26
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