LG AC / Heat Pump Error CH05 – Indoor Unit Not Receiving Outdoor Data
CH05: the LG indoor unit hears nothing back from the outdoor unit, so the compressor and outdoor fan stay off.
At a glance
Severity: Moderate
- Meaning
- Indoor Unit Not Receiving Outdoor Data
- Typical repair cost
- $0–$1,150
- DIY difficulty
- Easy
On LG ductless systems the cable between the two units does double duty: terminals 1 (L) and 2 (N) carry power, terminal 3 carries the data signal, and a separate ground rides along. The indoor unit logs CH05 when replies from the outdoor unit stop arriving on that terminal-3 line; the opposite direction, where the outdoor unit hears nothing from the indoor unit, has its own code, CH53. Because power and data share one cable, a single loose screw, a nicked conductor or a cable that doesn't meet LG's specification can kill the conversation while the indoor display still lights up. A dead outdoor supply and a surge-damaged outdoor inverter board or board fuse are the other big suspects. Owners typically first see CH05 after a power outage, a storm or a relocation of the equipment.
How it looks on the display
Model families & display variants
| Model family | Shows | Note |
|---|---|---|
| Wall-mount units with two-digit display (Art Cool and standard LG ductless) | CH / 05 | The display flashes CH and 05 alternately – read it as one code, not two. |
| Ducted, cassette and wall units on a wired remote | CH05 | Shown as a single code on the controller screen. |
| LG ThinQ Wi-Fi app | CH05 | Arrives as a push notification and stays in the error history, handy for telling the tech when it happened. |
| Multi F multi-zone systems | CH05 | Each head reports on its own; which heads show it tells you whether one line or the outdoor unit is at fault. |
Safety first · Consult a professional
Your part is the panel breaker and the outdoor disconnect – nothing behind a cover. Terminal 3 is not a harmless low-voltage wire, the block carries 208/230 V, and LG inverter boards stay charged for minutes after shutdown. Anything on the refrigerant side needs an EPA 608-certified technician.
- Unplug the appliance or switch off the breaker before opening any panel. Mains voltage can kill.
Symptoms
- Two-digit indoor display alternates between CH and 05
- LG ThinQ app sends a CH05 error notification
- Indoor fan blows room-temperature air while the outdoor fan and compressor never kick on
- On a Multi F system, either one head or every head reports the code
- Fault first showed up after an outage, a thunderstorm or after the unit was moved
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Conductors on terminals 1-2-3 loose, swapped or poorly stripped – typical after an install or relocation
- Outdoor unit unpowered – tripped breaker or pulled disconnect
- Outdoor inverter/main board or its fuse knocked out by a surge
- Interconnect cable damaged, or not the stranded, adequately sized cable LG calls for
- Indoor main board failure
- Boards out of step after a brief power glitch
- Interference on terminal 3 or a missing/poor ground connection
Fix it step by step
Confirm exactly what's displayed
Units with a two-digit display flash CH and then 05 in turn; wired remotes and the LG ThinQ app show CH05 as one code. Make sure you're not looking at CH53 – that's the reverse-direction fault, and the technician would start measuring at the other end.
Use the Multi F pattern
When a single head reports CH05 and the rest keep cooling, that head's own cable run or board is the prime suspect. If every head drops out together, the shared piece – the outdoor unit's supply, main board or fuse – is where to look.
Verify the outdoor supply
Check the outdoor unit's breaker in the panel and the disconnect box mounted beside the condenser. Inverter outdoor units may wait a few minutes after a cooling call before starting, so give it 3–5 minutes before deciding it's dead.
Tools: Flashlight
Hard-reset both boards
Stop the system with the remote, then open the breaker and the disconnect for at least 5 minutes. Once power is back, allow the boards a couple of minutes to handshake before you request cooling or heating.
Think back to recent work
A move, siding work or a replacement head means someone handled the conductors: a swapped 2 and 3, a stray strand or a reused solid-core cable can all produce CH05. Ask the installer to recheck the terminals against the wiring diagram – that's live-voltage work, not a homeowner job.
Log the timing for the tech
Write down whether CH05 appears the moment the unit powers up or only after it has run for a while, and screenshot the ThinQ error history. An instant fault leans toward wiring or a dead outdoor board, a delayed or intermittent one toward a loose terminal or a failing board.
How to reset CH05
- Stop the unit with the remote or in the ThinQ app
- Open the breaker and outdoor disconnect and leave them off for 5 minutes
- Close them again, wait 2–3 minutes, then restart in cool or heat mode
Where the parts are
- 1Fan
- 2Temperature sensor
- 3CAN bus
- 4Outdoor unit
- 5Compressor
- 6Engine computer (ECM)
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Reset breaker or outdoor disconnect | Yes | $0 |
| HVAC diagnostic visit | No | $100–$190 |
| Re-terminate or replace 1-2-3 interconnect cable | No | $160–$480 |
| Indoor main PCB replacement | No | $250–$600 |
| Outdoor inverter/main PCB (incl. fuse check) | No | $450–$1,150 |
Rough US estimates; technician call-out fees vary by region. Not a quote.
When to call a technician
Book an HVAC contractor who works on LG ductless equipment when CH05 survives a hard reset and the outdoor unit demonstrably has power. Checking terminal 3 means measuring on a cable that also carries 208/230 V, and on multi-zone systems the tech may need to read the outdoor board directly. On a recent relocation or install, the installer should recheck their own terminations first.
Frequently asked questions
What's the difference between CH05 and CH53?
Both say the units aren't talking, but they are reported from opposite ends. CH05 is logged when the indoor unit hears nothing from the outdoor unit; CH53 when the outdoor unit hears nothing from the indoor unit. That direction tells the technician where to start measuring.
Why does my display switch between CH and 05?
A two-digit display can't show four characters at once, so it alternates the prefix and the number. It is one fault, CH05, not two separate errors.
ThinQ sent me a CH05 alert while I was away – what now?
Switch the unit off in the app so it stops retrying. When you're home, check the breaker and outdoor disconnect and do one hard reset; if the alert comes back, book a technician and show them the error history.
We had the unit moved and now it shows CH05 – why?
A relocation means disconnecting and reconnecting terminals 1-2-3, often with new or extended cable. A swapped conductor, a screw that wasn't tightened or a splice added to reach the new spot are the usual culprits, so the installer should recheck the connections first.
Sources
- Official LG user documentation and support pages (facts only; wording is our own)
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy