LG air conditioner CH21 code: outdoor compressor or inverter fault (mini-split)

On LG mini-splits, CH21 points to a problem in the outdoor unit's compressor or its drive circuit. LG lists a temporary power issue, a faulty compressor, a drive or protection circuit error, or a bad electrical part in the outdoor unit.

Likely causes

Listed from most to least common.

1. Power surge, brownout or brief outage
2. Inverter (compressor drive) board fault in the outdoor unit
3. Compressor fault
4. Loose wiring in the outdoor unit

How to fix the CH21 code

Unplug the air conditioner or switch it off at the breaker before removing any panel or filter.

1. 1

   Step 1: Reset the power

   Switch off the breaker for the system, wait about 5 minutes, then switch it back on and restart the unit.

2. 2

   Step 2: Check for power problems

   Note if lights dimmed or other equipment reset when the code appeared. Tell the technician, as voltage problems can trigger CH21.

3. 3

   Step 3: Stop if it returns

   If CH21 comes back, leave the system off and book a repair.

When to call a technician

CH21 needs a licensed HVAC technician. The outdoor unit holds high-voltage parts that stay charged after the power is off, so do not open it.

A typical repair for this code costs $400–$2000 in the US, including parts and labor. Prices vary by area and model.

Models this applies to

• Ductless mini-splits (wall-mounted and Art Cool)
• Multi-zone mini-split systems
• Window air conditioners
• Portable air conditioners

Codes can differ slightly between models. Your owner's manual is the final word and is available from LG support.

Common questions