A CH21 error code on an LG air conditioner unit indicates that there is an issue with the voltage or current of the compressor or IPM module.
LG is known for manufacturing appliances that are durable and functional, and this reputation has carried over into their energy-efficient air conditioners.
However, even though these products are dependable, they still malfunction from time to time. An example of this is the CH21 error, which indicates that there is a problem with the compressor or IPM module of the unit.
Are LG air conditioners any good?
LG produces a host of home appliances, which includes their catalogue of portable, ductless, and window units.
Although the variety of different products that this brand offers is impressive, what really attracts customers to these products is the brand’s reputation for creating innovative and functional air conditioning units.
LG air conditioners are high-performing appliances that are durable enough to last for years, but the brand is also focused on increased energy efficiency.
As a result, models such as the Dual Inverter 22000 BTU LW2217IVSM and 14000 BTU LW1517IVSM are incredibly energy-efficient air conditioners.
CH21 error LG air conditioner
Even though the LG Dual inverter air conditioners, and even other models such as the 10000 BTU Smart Window Air Conditioner LW1017ERSM model, are so efficient in cooling the air in your house, it does not mean that they never have any errors.
The CH21 error code in LG air conditioners indicates that there is an error with the voltage or current relating to the inverter compressor or IPM module. Often, other error codes like CH22, CH26, and CH29 are related to this same issue.
There are various components that you need to check to find the source of this error, and this may require an electrical meter, like this Klein Tools MM300 Multimeter.
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Some of these checks include:
| Checks for the CH21 error | Components |
| Outdoor unit checks |
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| Noise filter and compressor component checks |
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| Inverter checks |
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Outdoor unit checks
The first thing to do when the CH21 error code appears is to ensure that the big switch on your external unit for the power supply is switched on. Also inspect the circuit breaker and power line to make sure they are undamaged.
If this switch is on, you can move on to checking the power supply in the outdoor unit as follows:
| Type of product | Ideal measurement | Condition |
| Single-phase product | 220 V, plus/minus 10 percent | For the L-N phase |
| Three-phase product | 380 V, plus/minus 10 percent | When two phases are measured, excluding the N-phase of the RSTN-phases |
| 220 V, plus/minus 10 percent | When two phases are measured, of the RSTN-phases, including the N-phase |
You can also come back to this unit after you have checked all the compressor components by switching off the power supply and disconnecting the wires from the bridge diode to perform the bridge diode test. This should measure between 0.4 V and 0.7 V for the RST black and red terminals.
Noise filter and compressor component checks
If the problem does not lie with the outdoor unit, you can also check the noise filter’s output voltage as follows:
| Type of product | Ideal measurement |
| For 208 to 230 V | 208 V to 230 V, plus/minus 10 percent |
| For 460 V | 460 V, plus/minus 10 percent |
Then, you need to disconnect the power to check some of the compressor components. First you have to check the compressor terminals for tightness using an Allen Wrench.
If this is also not the problem, you can move on to checking the following:
| Compressor component to be measured | Ideal measurement |
| The resistance of the compressor windings | For the UVW-phase 0.256 Ohms, plus/minus percent at 77 degrees |
| The inverter compressor insulation (windings to ground) | More than 10 Ohm |
Inverter IPM and PCB checks
If this is where the issue lies, you will see carbonisation, loose screws, or loose and damaged connector joint parts in the inverter PCB. You also need to measure the voltage of P and N of the inverter PCB DC link as follows:
| Type of product | Ideal measurement |
| Single-phase product | 310 V for the UVW-phase |
| Three-phase product | 540 V for the UVW-phase |
To check the inverter PCB, you need to look at the PCB LED-lights, which will be indicative as follows:
| LED-light colour | Meaning |
| Yellow | Main communication |
| Red | Represents the 10s case for errors |
| Green | Represents the 1s case for errors |