Temperature sensor
Common error-code part. Confirm resistance and connector style.
LG Window AC CH02 Error Code — Indoor Thermistor Fault
Your LG window air conditioner flashes CH02 on the display. The unit stops cooling. This is an indoor evaporator thermistor fault. Here is what it means and how to fix it yourself.
Quick Reference
| Code | Meaning | Severity | DIY Fixable? |
|---|---|---|---|
| CH02 | Indoor evaporator coil temperature sensor fault | Moderate | Yes — sensor replacement |
What CH02 Means
The CH02 error code tells you the evaporator coil temperature sensor (also called the indoor thermistor) is not sending a signal the control board can read. This sensor sits embedded in the evaporator coil fins. It tells the board when the coil is cold enough to start running the fan and when it is getting too cold and might freeze.
When this sensor fails, the control board cannot know the coil temperature. It shuts down the compressor and fan for safety. That is the CH02 error.
Parts and Tools You Will Need
- LG compatible indoor evaporator thermistor (check current price on Amazon)
- Digital multimeter with resistance mode (budget option on Amazon)
- Wire connectors or butt splices (on Amazon)
- Wire crimp tool (on Amazon)
- Small flathead screwdriver
- Phillips head screwdriver
Step-by-Step Fixes
Step 1: Power Cycle the Unit
Unplug the air conditioner from the wall outlet. Wait 10 minutes. Plug it back in. This clears transient errors that sometimes happen during brownouts or power surges.
If the CH02 code goes away and the AC runs normally, the sensor and board are fine. The issue was voltage fluctuation. If the code comes right back, move to Step 2.
Step 2: Check the Thermistor Wiring Connections
Unplug the AC. Remove the front grille and filter. Take off the metal control panel cover. Locate the evaporator coil — the cold finned section at the front of the unit. Follow the two small wires from the coil back to the control board connector.
Look for:
- Loose or disconnected wires
- Melted or corroded connectors
- Pinched or cut insulation
If you find a loose wire, reconnect it firmly. If you see corrosion, cut back to clean wire and use a butt splice connector.
Step 3: Test the Thermistor Resistance
Disconnect the thermistor from the control board. Set your multimeter to resistance (ohms, the Ω symbol). Place one probe on each thermistor wire.
At room temperature (around 77F / 25C), a good thermistor reads approximately 10,000 ohms (10kΩ). The exact reading varies slightly by temperature. Here are typical values:
- 50°F (10°C): ~40kΩ
- 77°F (25°C): ~10kΩ
- 95°F (35°C): ~5kΩ
If your reading is open (OL on the meter) or shorted (0 ohms), the thermistor is bad. If the reading is far outside the expected range (below 2kΩ or above 100kΩ at room temp), the thermistor has drifted out of spec.
Step 4: Replace the Indoor Thermistor
If the thermistor failed the resistance test, replace it.
- Unplug the AC
- Locate the thermistor embedded in the evaporator coil fins — it looks like a small bead or flat sensor on two wires, sometimes pushed into a metal clip or a plastic holder
- Note the routing of the wires so you can run the new one the same way
- Cut the old thermistor wires a few inches from the connector
- Strip 1/4 inch of insulation from the old wires and the new thermistor wires
- Connect using butt splices or wire connectors — match colors (usually both white, but some units use red and black)
- Insert the new thermistor bead into the same position on the coil
- Route wires away from the fan blade and any moving parts
Step 5: Check the Control Board
If the new thermistor did not fix the error, the control board itself may be at fault. This is less common but happens after a power surge or if the original thermistor shorted and damaged the board.
Before ordering a board:
- Inspect the solder joints around the thermistor connector on the board for cracks or burn marks
- Check for any bulging or leaking capacitors
- Verify you have 5VDC at the thermistor connector pins when the unit is plugged in (safety: do this carefully with the board powered)
If the board looks damaged, order an LG control board specific to your model.
Preventing Future CH02 Errors
- Keep the air filter clean — a dirty filter restricts airflow and makes the coil temperature fluctuate wildly, which stresses the sensor
- Avoid running the AC during brownouts or voltage dips
- Do not spray water directly into the unit when cleaning — moisture can reach the thermistor connector and cause corrosion
When to Call a Professional
Call a technician if:
- You replaced the thermistor and the board and the code still shows
- You are uncomfortable working with live electronics
- The unit is still under warranty — replacing parts yourself may void it