LG Inverter AC error code part-2

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In the previous article, we covered LG Inverter AC error code part-1 and covered some error codes, this continues with the previous article.

You can read the previous article by clicking here

If you missed part one and directly coming to this article then we will recommend you visit part -1 from the below link.

Fault Code 05

These error codes indicate a communication fault between the indoor and outdoor units; it appears approximately 5 minutes after powering up the system.
The communication between the units is a fluctuating DC voltage commonly called a serial signal, it can be easily lost if the wiring is not done correctly. If there is a communication error fault CH05 will appear on the Wired Remote within 5 mins of powering up the system.


First, check for any isolator or switches on the interconnecting cable and ensure both the Comms and Neutral are un-switched. Then confirm connections are correct and secure at both the Indoor and Outdoor units.
Check if any other devices are connected on the interconnecting cable, remove such equipment, and connect them elsewhere.
Open the outdoor unit to reveal the Main PCB and identify the Green and Red LED’s on that board. The Green LED should be lit steadily if power is present, the Red LED should be doing one of the following:-

  1. If the outdoor unit receives communications from the indoor unit, the Red LED should be flickering.
  2. If the Red LED glows steadily without flickering, then no communication is being received from the indoor unit. Check the interconnecting cables for any short or open circuits, not forgetting the connecting cables between the terminal rail and PCB on both Indoor & Outdoor units. Repair wiring, or replace the Indoor PCB as necessary.
  3. If the Red LED does not light at all, then the fault is with the outdoor PCB, or connections to it. Confirm that the Outdoor PCB is receiving power (Green LED lit). Repair wiring, or replace the Outdoor PCB as necessary.
  4. If Condition 3 above applies please check the following and repair/replace as required. Failure to do so may result in the new PCB becoming damaged.

a. Check PCB Control Fuse, if blown, identify cause and rectify.
b. Check Fan Motor(s).
i. AC Motors for Short Circuits or Down to Earth.
ii. BLDC Motors (See Product Technical Update – Sheet 83).
c. Reversing Valve Coil, for Short Circuit or Down to Earth.
d. Reactor, for Open Circuit.
e. Electronic Expansion Valve Down to Earth (See Product Technical Update – Sheet 96).
f. Compressor, for Short Circuit or Down to Earth.

LG Inverter AC

Additional Tests:

Set your meter to DC Volts, Test between terminals 2 and 3 of the outdoor unit and wiring terminals, you should see 0-75 Vdc, it will be fluctuating rapidly.
If this signal voltage is not present disconnect the wire from terminal 3 of the inter unit cabling, and test terminal 3 Voltage again. If Voltage is still not present, the outdoor PCB must be faulty. If this signal voltage is detected leaving the outdoor unit, reconnect wire 3 and check what is being received at the indoor unit. Disconnect wire 3 from the indoor terminal block and check the DC Voltage between this wire and terminal 2. It should be the same as what you saw at the outdoor unit, if not your wiring is at fault. With the wire still disconnected, check between terminals 2 & 3. You should see a relatively steady voltage in the range of 0.5 – 15Vdc (Negative). Any significant difference would indicate a faulty Indoor PCB.

Important: Comms Errors are also created on Universal “Synchro Systems” when they are not configured/commissioned correctly. Please follow the correct Synchro Commissioning Procedures.

Fault code 06

Is a problem with the Indoor unit coil outlet Thermistor Unplug the Thermistor from the indoor PCB and Check its resistance against this graph:

Alternatively the sensor can be tested while still connected to the PCB measure the DC voltage across the resistor and check it against the graph below.

Fault Code 07

On Multi split systems, the first unit switched on is the cool heat master, the master tells the condensing unit what to do. If the condenser is in heating and any slave is set to cooling a CH07 fault code will appear. Likewise if the condenser is in cooling and any slave is set to heating a CH07 fault code will appear. If the
master is switched off the next longest running unit becomes the master.

To clear the fault turn off the unit at the remote controller, turn it back on again and change the mode

Fault Code 09

Check for loose connections or dry joints where EEPROM connects on Main PCB, repair if possible, if not replace PCB.

Fault Code 10

Indoor Fan Motor problem, See Fault Code 67 for Troubleshooting help.

Fault Code 21

This fault is caused by an over current in the inverters DC power circuit. If the DC part of the circuit exceeds
14 Amps fault code 21 will be displayed.
This is caused by either the inverter PCB being faulty or compressor being short circuit or down to earth.

Disconnect the electrical connections to the compressor and check
the resistance of the compressor windings, measure from U to V, V
to W and W to U the values should be between 0.25 and 5 Ohms

The next test is to measure the resistance of the compressor
windings to earth.
Using a Megger (High Voltage Meter) measure the resistance from
any of the 3 compressor terminals to an Earth point (pipe work).
The value should exceed 2 M Ohms.

If the compressors fail these tests it will need replacing. If the compressor is OK you will need to check the inverter output voltages. Please see section on Inverter
testing at end.

Fault Code 22

This fault is caused by a Compressor over-current see code 21
Please see the section on Inverter testing at the end.

Fault Code 23

This fault indicates a fault in the DC part of the inverter circuit; it means that the Dc Voltage to the inverter is below 140 V Dc, it should be 370 V for single phase machines and 600 V dc for three phase machines. The fault is usually caused by the inverter charging resistor being faulty; this component is mounted on the outdoor unit PCB and cannot be replaced. Start the unit running and measure the DC Voltage supply to the inverter. This is easiest to measure at the inverter capacitors; it should be 370 V for single phase machines and 600 V dc for three phase machines See section on Inverter testing at the end.

we will keep posting the article on LG Inverter AC and will cover the rest of the error code, keep visiting our site.

Do let us know in comment section if yu have any questions related to LG Inverter AC.

Sayeeda Bano

Sayeeda is a passionate content writer having experience of more than 3 years in print media as well as electronic media. She has proved herself as the best orator and won the title of "Orator of the Year- 2013" from Oxford Speakers' Academy.

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