LG AC / Heat Pump Error CH38 – Causes & Fix
LG's protection stopped the system because the refrigerant level or pressure looks too low.
At a glance
Severity: High
- Meaning
- Low Refrigerant Protection – Leak Suspected
- Typical repair cost
- $100–$2,800
- DIY difficulty
- Hard
CH38 is LG's refrigerant-shortage protection. The outdoor board watches pressure and temperature data from the refrigerant circuit, and when the pattern says there isn't enough refrigerant circulating, it shuts the compressor off before it can overheat running half-empty. LG itself names two causes: not enough refrigerant after installation or reinstallation, and an unstable power supply that upsets the readings. In practice most real cases come down to a slow leak at a flare nut, a service valve that was never fully opened, or a long line set that was never given the extra charge it needs. If the code shows up once after a power dip and never again, the refrigerant is probably fine; if it keeps coming back, the circuit needs a certified technician.
How it looks on the display
Model families & display variants
| Model family | Shows | Note |
|---|---|---|
| Wall-mounted units with 2-digit display (Art Cool, standard models) | CH ↔ 38 | The indoor display alternates between CH and 38 because it can only show two characters at a time. |
| Units with wired remote or ThinQ app | CH38 | The full code appears on the remote screen or as a push notification with the error history in the app. |
| Multi-zone outdoor units | CH38 | Because the refrigerant circuit is shared, every connected head usually reports the code together; a leak at any branch can cause it. |
Safety first · Consult a professional
Refrigerant work – finding leaks, opening valves, adding charge – legally requires an EPA 608-certified technician. Many LG units use R-32, which is mildly flammable: ventilate the room and keep open flames and sparks away if you suspect a leak indoors. Leave the outdoor unit's covers closed; the inverter board holds a dangerous charge after power-off.
- Unplug the appliance or switch off the breaker before opening any panel. Mains voltage can kill.
- Sealed refrigerant system: repairs require an EPA 608 certified technician.
Symptoms
- CH38 on the wired remote or in the LG ThinQ app; on 2-digit displays, CH and 38 alternate
- Unit blows room-temperature air, then the outdoor unit stops
- Cooling or heating has been getting weaker for weeks before the code appeared
- Ice or frost on the thin copper line or the valves at the outdoor unit
- Oily, dirty stain at a pipe connection behind the indoor unit or at the outdoor service valves
- Code appeared soon after the system was installed, moved or serviced
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Slow leak at a flare connection, typical of rushed, DIY or reused-flare installs
- Undercharge – line set longer than the factory pre-charge covers, or charge lost during reinstallation
- Service valves at the outdoor unit not fully opened
- Unstable supply voltage (brownouts, generator, weak rural supply) disturbing the protection logic
- Leak in the indoor or outdoor coil, often corrosion pinholes
- Electronic expansion valve (EEV) stuck or a pressure/temperature sensor reading wrong
Fix it step by step
Do LG's power reset
Switch the unit off, then turn off its breaker for about 5 minutes and restart. LG recommends exactly this first; if the code was caused by a power hiccup, it won't come back.
Check the error history in ThinQ
If the unit is connected, open the LG ThinQ app and look at when CH38 appeared and how often. A single entry after a storm or outage is a very different story from a code that returns every afternoon.
Look for oil at the connections
Refrigerant leaks carry compressor oil, which collects dust. With a flashlight, check the flare nuts at the outdoor service valves and, if visible, under the indoor unit where the lines connect. Don't tighten or loosen anything – note what you see.
Tools: Flashlight
Think about the unit's history
Was it installed recently, moved to another room, or installed without a vacuum pump and gauges? Did the installer add refrigerant for the line length? Reinstallation without proper pump-down, new flares and evacuation is one of the most common routes to CH38.
Watch the power supply
Note whether lights flicker or other appliances reset when the code appears, and whether the unit shares a circuit with heavy loads. If voltage problems are suspected, an electrician can measure the supply under load.
How to reset CH38
- Turn the unit off with the remote or ThinQ app
- Switch off the unit's breaker for about 5 minutes
- Switch it back on and restart – if CH38 returns, keep it off and book a technician
Where the parts are
- 1Fan
- 2Temperature sensor
- 3CAN bus
- 4Outdoor unit
- 5Compressor
- 6Engine computer (ECM)
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Technician diagnostic visit | No | $100–$200 |
| Open service valves / add charge for long line set | No | $150–$450 |
| Flare or joint leak repair, evacuation and recharge | No | $350–$1,000 |
| Indoor or outdoor coil replacement | No | $1,200–$2,800 |
Rough US estimates; technician call-out fees vary by region. Not a quote.
When to call a technician
Call an EPA 608-certified HVAC technician or LG authorized service if CH38 returns after the 5-minute reset. The tech should find the leak with a detector or nitrogen pressure test, repair it, pull a deep vacuum and weigh in the charge – not just top it up. If the unit was installed recently, the installer should fix it under their workmanship warranty.
Frequently asked questions
Can I just add refrigerant?
No. You need EPA 608 certification to buy and handle refrigerant, and adding gas without fixing the leak only buys time. Most LG mini-splits are charged by weight, so the circuit has to be repaired, evacuated and recharged properly.
Why did CH38 appear after I moved the unit?
Moving a mini-split means recovering or pumping down the refrigerant, cutting new flares and evacuating the lines. If any of those steps is skipped, refrigerant is lost or a flare leaks – exactly what CH38 detects.
Can a power problem cause CH38?
Yes, LG lists unstable power as a cause. If the code clears after a reset and only returns during brownouts or storms, have the supply checked before assuming a leak.
Is it safe to keep running the unit?
No. CH38 exists to stop the compressor from running without enough refrigerant, which overheats it. Repeatedly restarting it can turn a flare repair into a compressor replacement.
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