LG Mini Split CH05 Error Code: Indoor and Outdoor Unit Communication Error (Meaning, Causes, Fixes)
What the code means
LG's US help library groups CH05 with CH53 and E0 and says these codes "indicate a communication problem between the indoor and outdoor units." In LG's R410A air conditioner service manual, error 05 is "Indoor & Outdoor unit communication error," with the error point "No signal communication between indoor & outdoor units"; the self-diagnosis table describes it as failing to receive the outdoor unit's signal on the indoor unit's circuit board. The unit stops operating while the code is shown. CH05 is different from CH53 (the outdoor main board failing to receive the indoor unit's signal) and from CH38 (low refrigerant), which appear in the same LG tables.
Likely causes
- A temporary communication or power glitch, which LG lists first and which a power reset can clear.
- The communication cable between the indoor and outdoor units not connected, loose at a terminal block, or shorted. LG's service manual lists both a disconnected and a short-circuited communication cable.
- A loose connection made during installation, which LG says is the usual cause when the code shows up shortly after the unit was installed.
- Power and communication cables run too close together, or a power supply wiring fault at the outdoor unit. LG's service manual lists both: not enough distance between the power and communication cables, and supply phase wiring errors.
- On systems with more than one indoor unit, auto addressing not completed. LG's manual says to check that auto addressing was done whenever CH05 appears.
- A failed communication circuit on the indoor or outdoor unit's main circuit board, which LG names as a cause in both its help article and service manual.
Safe DIY checks
Don't open the indoor or outdoor unit, touch the terminal blocks or replace boards yourself; LG warns that disassembling the air conditioner or replacing internal parts can cause fire, electric shock, serious injury or death. The outdoor unit carries line voltage even when the system isn't cooling, so turn off its breaker or disconnect before anyone works on it.
- Note when the code first appeared: right after installation or a move, or after the system had been running normally. LG's advice depends on which.
- If it appeared soon after installation, contact the installer. LG says this often means a loose connection from the install.
- If it appeared during normal use, unplug the unit or switch off its circuit breaker, wait about 5 minutes, then restore power and check whether the code has cleared.
- Check that the outdoor unit's breaker or disconnect hasn't tripped. LG's flowchart checks for main power at the outdoor unit before blaming the boards.
- If CH05 comes back after the reset, stop using the air conditioner and request LG service or a qualified HVAC technician.
🛠 When to call a pro
- CH05 returns after a 5-minute power reset. LG says to stop using the unit and contact LG support.
- The code appeared after installation or relocation. The installer should recheck the indoor-to-outdoor communication and power wiring at both terminal blocks.
- Testing the communication line. LG's service manual says communication is normal when the DC voltage between the communication terminals fluctuates within about -9 V to +9 V; a technician uses this to tell an indoor board fault from an outdoor board fault.
- On multi-zone systems, LG's flowchart asks whether every indoor unit shows CH05. If only one does, the technician checks that unit's communication cable and then its board; if all do, the outdoor unit's power, LED and board are checked first.
- Any circuit board replacement, which LG's manual says to do only after the wiring and power checks.
Parts that commonly fix it
Always match the part number to your exact model.
Indoor or outdoor unit main control board
Only after a technician has confirmed the communication cable, power supply and signal voltage are good; match the exact LG model number.
Search eBay →Mini split communication / interconnect cable
If the cable between the indoor and outdoor units is damaged or shorted; use the wire type and gauge in your LG installation manual.
Search eBay →Multimeter
For a technician checking power at the outdoor unit and the DC signal on the communication terminals.
Search eBay →Sources
Last reviewed 2026-10-24. Always confirm against the manual for your exact model number.