- HVAC
- Air conditioner
CH66
LG CH66 on an air conditioner: indoor to outdoor connection fault
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
CH66 means the unit detects a problem with the communication line or the piping connection between the indoor and outdoor units. If it appeared after installing or moving the unit, call the installer; if it appeared during use, reset once from the breaker.
Safety first
Stop and check this first
- LG warns not to disassemble the air conditioner or replace internal parts yourself, as doing so may cause fire, electric shock, serious injury or death. If the same code returns after the reset, stop using the unit and request service to prevent further damage.
- If CH66 appears right after an installation or relocation, LG refers you to the installer: ask them to inspect it before paying for another visit, because the connection between units was part of their work.
Safe checks you can perform
- Confirm the code on the display
- Recall any installation or relocation
- One reset from the circuit breaker
- Inspection of the line and connections between units
Leave these tasks to a qualified professional
- Do not attempt this professional task: Check the piping connection with a leak test
- Do not attempt this professional task: Final run without the code
- Do not attempt this professional task: Check communication between the units
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Check the piping connection with a leak test
What they doIf CH66 appeared after installing or moving the unit, the technician inspects the refrigerant connections and runs a leak test with a detector.
They must show youthe pressures in the operating mode and the detector result at each joint.
In writingthe leak test result and, if refrigerant was recovered or charged, the kg and type.
Final run without the code
What they doAfter the repair, the technician runs the unit in cooling and, for a heat pump, in heating until CH66 is confirmed not to return.
They must show youthe unit running in each mode with no CH66 on the display.
In writingthe modes tested, the length of the test run and the date.
Check communication between the units
What they doThe technician measures the voltage between the connection terminals of the indoor and outdoor units and inspects the communication cable before considering boards.
They must show youthe voltage measured between terminals and the condition of the cable and each connection.
In writingthe CH66 code, the measurements, what was corrected or which part was replaced and why, and the date.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Confirm the code on the display
- Who:
- you.
- How:
- look at the indoor unit display: LG places the letters CH before the code numbers. If only the lamp blinks, note how it blinks and which mode the unit was in.
- Result that matters:
- that the code is CH66 and not another one from the same guide (CH05 and CH93 are also communication codes).
- If it is CH66:
- continue with this page.
- If it is another code:
- look up that code, because the cause and steps change.
- Evidence to keep:
- a photo of the display with the code, date, time and operating mode.
Evidence: LG Air Conditioner - Guide to Error Codes
Recall any installation or relocation
- Who:
- you.
- How:
- think about whether the unit was installed, moved or had its connecting line touched shortly before CH66 appeared. LG treats these cases separately from normal use.
- Result that matters:
- whether CH66 appeared after installation work or during normal use.
- If it was after installing or moving the unit:
- do not keep resetting, call the installer; their details are usually on their business card or on the side of the unit.
- If it was during normal use:
- go on to the breaker reset.
- Evidence to keep:
- the date of the installation or move, the installer's name and the date of the first CH66.
Evidence: LG Air Conditioner - Guide to Error Codes
One reset from the circuit breaker
- Who:
- you.
- How:
- switch the unit off with the remote, unplug it or turn off its circuit breaker, wait about 5 minutes as LG states and restore power. Do it only once for CH66.
- Result that matters:
- whether CH66 comes back at start-up or after a while.
- If it clears and the unit runs normally:
- note the date; if it returns, request service with those dates.
- If it returns:
- LG says the unit needs inspection by a service technician; do not repeat resets.
- Evidence to keep:
- date and time of the reset, the mode it was in (cooling or heating) and whether CH66 came back.
Evidence: LG Air Conditioner - Guide to Error Codes
Inspection of the line and connections between units
- Who:
- certified refrigerant and HVAC technician (F-gas certified in the EU).
- How:
- with power isolated, inspect the communication cable and its terminals on both units and the refrigerant piping connections between the indoor and outdoor units.
- Result that matters:
- where in the connection between units the fault behind CH66 is.
- If a loose terminal, a damaged cable or a poor connection is found:
- it is corrected and the unit is tested.
- If everything is correct:
- the technician continues with the electrical and refrigerant measurements for the model.
- Evidence to keep:
- a job sheet listing what was inspected and photos of the terminals and connections.
The terminals between units carry mains voltage and the pipes hold pressurised refrigerant (R32 is flammable): certified technician only.
Evidence: LG Air Conditioner - Guide to Error Codes
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- HVAC
- Brand
- LG
- Product type
- Air conditioner
Known code variants
- CH66
- error 66 aire LG
- LG AC error 66
- LG CH 66
- LG CH66
What it means
In LG's air conditioner error code guide (Help Library, covering split and window units), CH66 is a feature of inverter models that detects communication or piping connection issues between the indoor and outdoor units. LG separates two cases: right after installation or relocation, contact the installation technician; during normal use it may be a temporary fault caused by unstable power. LG notes the guide was written for all models, so content may differ from your product. The code alone never proves that a part is faulty.
Warnings and stop conditions
- Higheditorial warning
LG warns not to disassemble the air conditioner or replace internal parts yourself, as doing so may cause fire, electric shock, serious injury or death. If the same code returns after the reset, stop using the unit and request service to prevent further damage.
Evidence: How to Troubleshoot Error Codes CH01, CH02, CH06 on Your LG Air Conditioner
- Mediumsource verified
If CH66 appears right after an installation or relocation, LG refers you to the installer: ask them to inspect it before paying for another visit, because the connection between units was part of their work.
Evidence: LG Air Conditioner - Guide to Error Codes
Symptoms and causes
Probable causes · in order
- Recent installation or relocationCommon
LG says that if CH66 appears right after installing or moving the unit, the origin lies in the communication or piping connection made during that work.
Evidence: LG Air Conditioner - Guide to Error Codes
- Unstable power supplyPossible
If CH66 appears during normal use, LG attributes it to a temporary fault from unstable power or other electrical factors, which a reset may clear.
Evidence: LG Air Conditioner - Guide to Error Codes
- Communication line or connection between unitsPossible
If the code persists after the reset, LG calls for inspection by a technician: the line between units or the piping connection may be defective.
Evidence: LG Air Conditioner - Guide to Error Codes
Virtual technician
Does CH66 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
LG Air Conditioner - Guide to Error Codes
LG Electronics · 2026 · official_doc
- 2
How to Troubleshoot Error Codes CH01, CH02, CH06 on Your LG Air Conditioner
LG Electronics · 2026 · official_doc
Was this entry useful?