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

  1. Power off the AC at the breaker or unplug it for 5‑10 minutes
  2. Ensure outdoor unit has clear airflow and no debris blocking condenser
  3. Clean or replace air filters
  4. Restart the unit and observe if CH21 persists

Technician Only Professional diagnostics and repair

  1. Measure compressor current draw and compare with specification
  2. Inspect inverter PCB/IPM and outdoor unit wiring for damage or shorts
  3. Check compressor windings and insulation resistance
  4. Assess refrigerant levels and outdoor unit thermal performance

Parts needed: inverter PCB/IPM module, compressor, wiring/connectors, capacitor (if applicable)

🛑 When to Call a Pro:
  • CH21 persists after reset and filter/airflow checks
  • Signs of electrical burning, unusual noises, or repeated tripping

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

Data last verified: 2026-07-07

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