I have an LG Mini Split AC Model LSN303HLV. It shuts off and displays CH38 on the small display screen. I'm assuming it's an error code, but I couldn't find it online. Any advice, please?

Find a new AC engineer approved by LG. All AC Units leak a small amount at the compressor bearings and seals. It sounds like yours needs some sealant. and gas, or a new sensor. Diagnosis by an LG trained engineer is needed.

https://www.google.com/search?q=3+zone+LG+mini+service+engineer

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LG Split System Air Conditioner Error code = CA or CH10
LG AC Fault Definition = Discharge temp more than 130 °C - Faulty discharge thermistor
Flashing Light = 10
Display = Indoor Outdoor
Indoor Operation = ON

Full list of Gree Air Conditioner Mini Split Units Fault Codes. When error codes appear on the Gree air conditioner indoor display, this tells the user there is an issue with the Gree AC unit. The error code displayed will inform you of the issue or problem that is occurring with the air conditioner. Knowing what the error code means and its definition will help you to understand and troubleshoot the exact Gree air conditioner part that needs to be fixed, cleaned, repaired, or replaced. You can then clean, fix, or replace the Gree part yourself and save money. See below for all error codes that can occur on Gree Mini Split AC's.
Gree Mini Split Air Conditioner Error Codes - How To Fix
Gree Viero AC Mini Split PDF Owners and Troubleshooting Manual
GREE DUCTLESS AIR CONDITIONING & HEATING SYSTEM INSTALLATION MANUAL

Gree Mini Split Air Conditioner Part Names and Locations
INDOOR AND OUTDOOR UNIT
The Gree Air Conditioning Vireo System has onboard error code diagnostics. The outdoor unit will provide status indicators and the indoor wall unit and remote control will display error codes. The following is a summary of the codes with explanations...
GREE AC DIAGNOSTIC ERROR CODES
Gree Vireo Mini Split Air Conditioner Error Code F0
Refrigerant Leakage Protection
1) Refrigerant leak(s).
2) Indoor coil temperature sensor not calibrated.
3) Refrigerant flow is restricted (ex. valve, exv, debris)
Outdoor Unit Red Light Indicator - 9 flashes and 1 sec Off
Gree Vireo Mini Split Air Conditioner Error Code E1
System High Pressure
1) Over charged with refrigerant.
2) Blocked or dirty outdoor coil.
3) Extreme outdoor ambient conditions
Gree Vireo Mini Split Air Conditioner Error Code E2
Indoor Anti-Freeze Protection
1) Low return airflow.
2) Indoor fan speed is too low.
3) Indoor coil is blocked or dirty.
Outdoor Unit Yellow Light Indicator - 3 flashes and 1 sec Off

Gree Vireo Mini Split Air Conditioner Error Code E4
Compressor High Discharge Temperature Protection
Please refer to the malfunction analysis (discharge temperature, overload) in service manual.
Outdoor Unit Yellow Light Indicator - 7 flashes and 1 sec Off
Gree Vireo Mini Split Air Conditioner Error Code E5
Overcurrent Protection
1) Supply voltage is unstable.
2) Supply voltage is too low and system load is too high.
3) Indoor coil is blocked or dirty.
Outdoor Unit Yellow Light Indicator - 5 flashes and 1 sec Off
Gree Vireo Mini Split Air Conditioner Error Code E6
Communication Malfunction
1) Communication cable is wired incorrectly between indoor and outdoor units.
2) Indoor or Outdoor control board malfunction.
Outdoor Unit Yellow Light Indicator - Continuous On
Gree Vireo Mini Split Air Conditioner Error Code E8
High Temperature Resistant Protection
1) Incorrect refrigerant charge level.
2) Refrigerant metering device malfunction.
3) Compressor malfunction.
Outdoor Unit Yellow Light Indicator - 6 flashes and 1 sec Off
Gree Vireo Mini Split Air Conditioner Error Code EE
EEPROM Memory Malfunction
Control board malfunction.
Outdoor Unit Yellow Light Indicator - 11 flashes and 1 sec Off
Gree Vireo Mini Split Air Conditioner Error Code C5
System Configuration Malfunction
1) No jumper cap inserted on the control board.
2) Incorrect or damaged jumper cap on control board.
3) Indoor and outdoor units are not compatible.
Gree Vireo Mini Split Air Conditioner Error Code Fo
Pump Down or Gathering Refrigerant Status
Optional Service Mode
Outdoor Unit Yellow Light Indicator - 17 flashes and 1 sec Off

NOTE: All of the Gree Air Conditioner Model Numbers below are applicable for the error codes on this page...
Gree AC Vireo Models: VIR09HP115V1A, VIR12HP115V1A, VIR09HP230V1A, VIR12HP230V1A, VIR18HP230V1A, VIR24HP230V1A, VIR30HP230V1A, and VIR36HP230V1A.
Gree Mini Split Air Conditioner Error Code Charts
Gree Mini Split AC Remote Control Button Names
Gree Mini Split AC Remote Control Icons Display Screen

Gree Mini Split Air Conditioner Air Filter Cleaning Procedure
Gree Viero AC Mini Split PDF Owners and Troubleshooting Manual
GREE DUCTLESS AIR CONDITIONING & HEATING SYSTEM INSTALLATION MANUAL
Need help with error codes on your Gree AC? Please leave a question below and we will be happy to help.

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I assume it is a LG as you did not state: Try these links:

http://www.refrigeration-engineer.com/forums/showthread.php?20036-Need-help-trouble-shooting-mini-split-ac-error-code-quot-e4-quot

Anyone familiar with LG portable AC units Consumer Electronics Bob Is The...

LG Portable Air Conditioner Error Code

LG Window Air Conditioner Error Codes Sears PartsDirect

e4 error code comes for defrost. just remove the cover of your split ac, you shell found a sensor there , check for rat cut.

How do i fix an error 10 CH