HOW TO

LG Inverter AC error code part-3

September 28, 2021September 28, 2021 Sayeeda Bano 0 Comments ch105, ch24, ch25, ch26, ch27, ch28, ch29, ch32, ch33, ch39, ch40, ch41, ch44, ch45, ch46, ch47, ch48, ch51, ch52, ch54, ch60, ch61, ch62, ch65, ch67, ch73, LG Inverter AC

If you are reading LG Inverter AC article first time and you should check part 1 and part 2.

LG Inverter AC error code part-1

LG Inverter AC error code part-2

Fault Code 24

If the unit has a low or high pressure fault CH24 will display.
If the LP switch goes open circuit the compressor will be stopped, on inverter units this can take up to 30 seconds. The LP Switch goes open circuit when the suction pressure falls below 0.5 bar the Hp Switch opens at 41 bar.
The fault code will only occur if the pressure switch is tripped 5 times within 1 hour, this can only be reset by switching off the power to the condensing unit for 2 minutes. If your unit does not have any pressure switches it may still have a plug on the outdoor unit PCB labelled CN Press, it should have a link plugged in, if the link is missing it must be replaced.

Fault Code 25

This fault indicates a problem with the incoming power supply to the system.
Measure the Voltage of the incoming supply, if it is less than 140V AC or greater than 300V AC this fault will occur.
If the Power supply is correct and the fault persists replace the outdoor unit PCB.

Fault Code 26

This fault indicates a problem with the positioning system of the inverter compressor, which indicates a seized compressor.
Firstly check the compressor is correctly connected. Next reset the power supply to the system ensuring the power is left off for 5 minutes. Start the unit up, after a couple of minutes the compressor will try and start, you can hear a high pitched whine when it does. If the compressor does not start turning within a couple of seconds the whining will stop. The compressor will try to start 3 times then the fault will recur.

Fault Code 27

This fault indicates a problem with the inverter module, see section on testing inverters. Also check reactor is connected to the PCB and check its resistance it should be well under 1 Ohm.

Fault Code 28

This fault indicates a problem in the DC part of the inverter circuit; it means that the DC Voltage to the inverter is too high.

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 end.

Fault Code 29

Check and correct for any:

Overload operation (Pipe restrictions / Restricted Airflow / EEV defect / Refrig. Overcharged)
Compressor damage (Insulation damage / Motor damage)
Input Voltage Low
ODU Inverter PCB assembly damage

Fault Code 32

LG Inverter AC Indicates that the Inverter compressor discharge temperature is high (above 105ºC) this usually indicates the system has either a shortage of refrigerant or a blockage in the system.
Reset the power to the unit for 2 minutes and restart it. If the compressor starts measure the compressor discharge temperature, typically it should not be more than 50ºC above the ambient temperature around the condensing unit. It may take quite a long period for the compressor to overheat so don’t just start the unit and run. Make sure you check the unit is operating correctly and providing adequate cooling.

Fault Code 33

LG Inverter AC Indicates that the fixed speed compressor discharge temperature is high (above 105ºC) this usually indicates the system has either a shortage of refrigerant or a blockage in the system. Reset the power to the unit for 2 minutes and restart it, If the compressor starts measure the compressor
discharge temperature, typically it should not be than 50ºC above the ambient temperature around the condensing unit. It may take quite a long period for the compressor to overheat so don’t just start the unit and run. Make sure you check the unit is operating correctly and providing adequate cooling.

Fault Code 39

Check and repair or replace as necessary:

PCB defect / Wiring defect
Different Micom Software Version
ODU Inverter PCB assembly damage

Fault Code 40

This fault indicates a problem with the current drawn by the AC part of the inverter circuit.
Refer to the inverter testing procedure at the end.

Fault Code 41

This fault indicates an Inverter Compressor discharge Thermistor fault
Unplug the Thermistor and Check its resistance check 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 44

Indicates a fault with the Outdoor unit air Thermistor Unplug the Thermistor from the PCB and Check its resistance check 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 45

LG Inverter AC Indicates a problem with the condenser 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 46

LG Inverter AC Indicates a problem with the compressor suction 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 47

LG Inverter AC Indicates an Inverter Compressor discharge Thermistor fault Unplug the Thermistor from the PCB and Check its resistance check 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 48

This fault indicates that the compressor discharge sensor and the condenser air temperature sensors are both unplugged. Both these sensors are connected to a single connector on the outdoor unit PCB, plug it in and the fault will go away.

Fault Code 51

LG Inverter AC indicates that the capacity of the indoor unit / units is too great for the condensing unit. Make a note of the model number of the fan coil/coils and the condensing unit and check with the equipment supplier that the units you have installed can be connected together.

Fault Code 52

This fault code indicates a communication error between the Main and Sub micom (CPU’s) on the outdoor unit main PCB. Check for evidence of damage, if none found reset power, if fault reappears replace pcb.

Fault Code 53, (see fault code 05)

Fault Code 54

This fault normally indicates a lost phase or the phases are reversed on the power supply to 3 phase units.
Check all 3 phases are available at the power terminals to the unit. You should have 415v AC across red to blue, blue to yellow and red to yellow,
If this is all ok turn off the power and swap the red and yellow cores of the power supply cable over, reset the power and the unit will operate.

Fault Code 60

Check the correct PCB assembly has been installed, check for dry joints, replace outdoor unit PCB if nothing
is found.

Fault Code 61

Indicates the outdoor unit condenser coil temperature is high above 65ºC, this will usually be experienced in cooling mode and will indicate insufficient air being drawn over the coil.
Check there are no blockages to the coil (carrier bags dirt etc); check the air flow is not short circuiting from the front to the back of the unit and check for Nitrogen in the system.

Fault Code 62

Indicates the outdoor unit Inverter heat-sink thermistor has detected that the heat sink is overheating 85ºC.
This is usually caused by debris blocking the heat-sink fins or an error with the thermistor, see code 65.

Fault Code 65

Is a problem with the Inverter PCB heat sink thermistor for the heat sink on the outdoor unit PCB, unplug the Thermistor from the 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 67

This is a problem with the Outdoor Fan Motor, where rotation is not detected, and could be the result of either Mechanical or Electrical failure.

Check that motor is free to rotate and not seized.
 Check the motor is electrically sound, windings not Open or Short circuit.
 Check power output from PCB to fan motor.
 Check rotation feedback circuit.

More modern units use inverter fan motors, which are powered by a DC Voltage.
In reality these fan motors are AC fan motors with a small inverter-type circuit build inside. This inverter circuit is integrated with the fan motor and impossible to replace, you have to replace the entire fan motor. Similar to inverter-controlled compressors, the speed of these fan motors can be changed to whatever is needed (within certain limits). In practice the change in fan speed is not ‘continuous’ but certain fixed speeds
have been programmed inside the AC unit. This type of fan control can be recognized by the 5 wires coming from the fan on a connector with 7 possible connections These fan motors have 5 connections, power supply is 360VDC, and the speed is determined by a voltage ranging from 0 (0 rpm) to 5VDC (max speed) and a power supply for the internal electronics of 15VDC. These motors are easy to identify from a wiring diagram, they always show them not connected to anything as the electronics are too difficult to draw on the diagram.

Detail of Hall Sensors

A Hall effect sensor works like a magnetic reed switch, one end is wired to a 15 Vdc supply and the other is the feed back to the PCB. As a magnet mounted on the rotor of the motor passes the hall sensor the reed switch closes momentarily and allows the DC signal to flow through it back to the PCB. The hall sensors have a resistance so the voltage fed back to the PCB will only be approximately 12V DC.
The pcb will know what speed the fan motor should be turning as it is also controlling the output of the inverter, if there is a discrepancy between the inverter output RPM and the feedback from the hall sensors a fault will occur. Usually the fan will rev very fast for a few seconds then stop this indicates hall sensor problems. Replace either Motor or Fan PCB as necessary.

Fault Code 73

Check and repair or replace as necessary:

Overload operation (Pipe restrictions / Restricted Airflow / EEV defect / Refrig. Overcharged)
Compressor damage (Insulation damage / Motor damage)
Input Voltage abnormal
Power supply wiring abnormal
Inverter PCB assembly damage

Fault Code 105

This is due to a Communication error between the Main outdoor PCB and Fan PCB.
 Check for Open/Short of communication line between the Main and Fan PCB’s.
 Check communication cable plug connections.
 Is the communication LED on?

Testing Inverters

It is best to test inverters with no compressors connected especially if you expect the compressor is at fault. But if you remove the wires from the compressor and try to run the systems a fault will be displayed. The fault is caused by the inverter PCB being able to detect whether a compressor is connected or not. Most modern inverters are able to detect whether the compressor has been disconnected in only a few seconds making
testing very difficult.

Testing can be done in two ways:

You will need a digital multi meter with a min max function,
Turn off the power
Disconnect the compressor either from the PCB or at the compressor terminals.
Connect your meter to two of the phases (Red to blue) set your meter to record max and min voltage
Power up and Start the unit
Let the inverter start and watch the Voltage rise
Record the maximum Voltage
The inverter will stop after a few seconds and the voltage will fall to 0
Swap the leads to measure the next two phases (Red to Yellow).
Measure as before
Repeat for the last two phases Blue to Yellow.
The readings of maximum voltage should be the same for all 3 measurements if not the inverter is faulty, the
PCB will need replacing.
If the readings are equal the Inverter is healthy and the compressor will need replacing.

Hard way

You will need a digital multi meter with a min max function,
Turn off the power
Disconnect the compressor either from the PCB or at the compressor terminals.
Connect your meter to two of the phases (Red to blue) set your meter to record max and min voltage
Power up and Start the unit
Let the inverter start and watch the Voltage rise
Record the maximum Voltage
The inverter will stop after a few seconds and the voltage will fall to 0
Swap the leads to measure the next two phases (Red to Yellow).
Measure as before
Repeat for the last two phases Blue to Yellow.
The readings of maximum voltage should be the same for all 3 measurements if not the inverter is faulty, the
PCB will need replacing.
If the readings are equal the Inverter is healthy and the compressor will need replacing.

Easy way

You will need an LG Inverter tester,
Turn off the power
Disconnect the compressor lead from the compressor terminals.
Connect your inverter tester to all 3 leads (polarity is not important)
Power up and Start the unit
Let the inverter start and watch the led’s
All 6 must light up and should be of equal brightness
The inverter will stop after a few seconds and the led’s will go out
If you miss the led’s (they will only light for a couple of seconds) the unit will try to start again 3 times with a 3
minute delay between each test
If all 6 led’s DON’T light up the inverter is faulty, the PCB will need replacing.
If the led’s all light up the Inverter is healthy and the compressor will need replacing.