LG CH21, CH23, CH26 and CH29: the outdoor compressor and board group
LG places CH21, CH23, CH26, CH29 and E9 in one group: a problem with the outdoor unit compressor or circuit board. Here is what that category is telling you.
What this means
LG's help-library article assigns CH21, CH23, CH26, CH29 and E9 to a single category: a problem with the outdoor unit compressor or circuit board. That is a narrower statement than it appears, because it moves the fault out of the indoor unit and out of the sensing group and places it in the inverter drive and compressor side of the system.
Equipment and model context
LG residential air conditioners covered by the United States help-library article grouping these codes as outdoor compressor or circuit board problems
- LG single-split outdoor units
- LG multi-split outdoor units
- LG inverter heat pump outdoor units
What is quoted below is the category LG gives home customers in its United States help library, and nothing finer. LG service literature publishes fuller definitions for each of these codes, and the meaning of a CH number on LG commercial or variable refrigerant flow equipment is taken from that product's own manual rather than from this article.
What you may notice
- The outdoor unit starts and stops abruptly, or never starts, while the indoor unit continues to run its fan.
- The code appears reliably during the first seconds of a start attempt rather than after a period of running.
- Household lighting or another motor appliance reacts at the instant the outdoor unit tries to start.
Likely causes
- An inverter drive can detect current or bus voltage outside the range it will operate in and stop within a fraction of a second.
- A compressor that is difficult to start, including after refrigerant has migrated into it during a long idle period, presents the drive with a load it refuses.
- Supply conditions at the outdoor unit, including voltage that sags under starting load, can take the drive outside its working window without any component failing.
Diagnostic paths
The outdoor unit fails at the same point every time
Each start attempt ends after a similar interval, and the timing is consistent enough that you can predict when the unit will stop.
Count the seconds and record the figure. A repeatable failure window is the most useful single number an owner can give an engineer for this group of codes.
It follows a season of the system standing unused
The equipment has been switched off for months and the code appears on the first attempt to use it again.
Leave the isolator on and the operation off for several hours before trying again, so any crankcase heating arrangement can work as designed.
Lights dim or another appliance stutters at the moment of start
Something else on the property visibly reacts at the exact instant the outdoor unit attempts to start the compressor.
Report which circuits react. Supply behaviour under starting load belongs to the electrical installation as much as to the air conditioner.
Speed explains the character of this group. An electrical protection defends semiconductors that fail in a fraction of a cycle, so the drive stops on the measurement itself and reports afterwards rather than watching a value drift.
- MeasurementCurrent or bus voltage leaves its band
- Immediate stopThe drive shuts down within milliseconds
- Code raisedThe event is reported after the fact
- No warningThere is no gradual loss of output first
| Area | In or out | Why it matters to you |
|---|---|---|
| Indoor sensing | Out | The indoor unit is not the suspect |
| Outdoor drive and board | In | The repair is at the outdoor unit |
| Compressor | In | The costliest component is in scope |
| Supply to the unit | Considered alongside | An electrician may be involved |
A category that narrows the bill as well as the fault
Nobody enjoys reading that a code concerns the compressor, and it is worth being straight about why the category matters anyway. Indoor-side faults tend to be the shorter visit and the smaller part, and knowing which half of the system LG places the code in tells you which conversation you are about to have. It also tells you where an engineer will spend their time.
The category does not sentence the compressor. LG names the compressor or the circuit board in the same breath, and drive electronics, sensing on the drive, and supply conditions all sit inside that phrase. A compressor is replaced on measurements, not on a code, and any quote that skips the measurement step is worth questioning.
The retry rule is stricter here than it looks
LG allows one power interruption of about five minutes and then instructs the owner to stop using the product if the same code returns. For an electrical protection that instruction has more force than it does for a sensing code. Every extra start attempt puts the power stage through the same event that stopped it, and if the compressor is mechanically hard to start, each attempt asks a struggling motor to break away under full drive.
Restraint is the practical advice: one attempt, careful observation, and then stop. Where the system has stood idle for a long period, leaving power connected while keeping operation off is worth several hours before the next try. The crankcase heater guide explains why that wait exists, and the inverter technology explainer covers what the drive is doing between the supply and the motor.
What to give the technician
Give the engineer the outdoor and indoor model numbers, the exact CH code, how many seconds the unit ran on each attempt, how long the system had been idle, and whether household circuits reacted at start.
Safe homeowner checks
- Make one start attempt after LG's five-minute power interruption, and count how many seconds the outdoor unit runs before it stops.
- Observe whether the outdoor fan turns at all during the attempt, from a safe distance and without touching the guard.
- See whether a breaker or fuse serving the outdoor unit has tripped, and whether anything else in the property is misbehaving at the same time.
Is a reset appropriate?
One interruption of about five minutes is what LG publishes. Because this group covers an electrical protection, repeating it after the code returns risks converting a diagnosable fault into a replacement.
When to call a technician
- LG instructs the owner not to disassemble the unit or replace internal parts, warning of fire, electric shock, serious injury, or death.
- Measuring compressor windings, inverter output, and supply voltage under load are energised tasks inside the outdoor enclosure and belong to a qualified engineer.
Questions people ask about this
Does LG CH21 mean I need a new compressor?
LG's category names the outdoor compressor or circuit board together. Drive electronics, sensing on the drive, and supply conditions sit inside the same phrase, and a compressor is condemned on measurements rather than on a code.
Why does the indoor fan keep running?
The indoor unit has not faulted. It continues to circulate air while the outdoor unit is stopped, which is why the room can feel unchanged even though no cooling or heating is being produced.
Can an electrical supply problem cause these codes?
Voltage that sags under starting load takes the drive outside the window it will operate in, which produces a protective stop with no component fault. That is why the installation is examined alongside the equipment.
Evidence recordHow this page was checked
official manufacturer support article, service manual · checked 2026-09-15
Every technical claim above was written from primary documentation held in the HVAC Bench evidence record: LG Electronics technical literature. Where a source limits a definition to certain models, test conditions, or product classes, that limit is repeated here rather than generalised.
- Documentation class
- official manufacturer support article, service manual
- Scope of the definition
- LG residential air conditioners covered by the United States help-library article grouping these codes as outdoor compressor or circuit board problems
- Last checked
- 2026-09-15