What the CH01 error code means

Every LG split AC has a small thermistor sensor mounted near the return-air grille inside the indoor unit. This sensor continuously measures the room temperature and sends the reading to the control board, which uses it to decide when to ramp the compressor up or down and when to cycle off once the set temperature is reached.

When the board detects that the sensor circuit is either open (disconnected) or shorted (resistance near zero), it raises CH01 and stops the compressor. On most models the indoor unit's LED will blink once to confirm this code. The indoor fan may keep running, but cooling will not work.

Note: CH01 is sometimes displayed as C1 on older LG models. The meaning and fix are the same.

Common causes of CH01

The most frequent cause is simply a loose connector — the sensor plug has vibrated free from the PCB header over time. After that, a genuinely failed thermistor (usually from age or a voltage spike) is the next most common. Wiring damage is less likely but possible if the indoor unit was recently serviced and a wire was pinched during reassembly.

Step-by-step fix

Before starting, switch the AC off at the circuit breaker — not just the remote — and wait at least one minute.

  1. Open the indoor unit front panel. Most LG indoor units have clips at the sides; lift the panel up until it locks in the raised position.
  2. Locate the room sensor. Follow the return-air grille inward. The sensor is a small bead or capsule on a two-wire lead, usually clipped to the filter frame or hanging just behind the grille.
  3. Check the connector. Trace the sensor wire to where it plugs into the main PCB. Unplug and re-plug it firmly. Look for corrosion or bent pins.
  4. Test the sensor with a multimeter. Set the meter to resistance (ohms). At 25 °C, a standard LG room thermistor reads approximately 10 kOhm. At 30 °C it drops to about 8 kOhm, and at 20 °C it rises to about 13 kOhm. If you get an open-line reading (OL) or near zero, the sensor is faulty.
  5. Replace if necessary. LG room sensors are inexpensive and widely available. Match the part to your model number, clip the new sensor into position, and plug it in.
  6. Restore power and test. Turn the breaker back on, start the AC, and confirm CH01 does not return.

Tip: If CH01 appeared right after a filter cleaning, you may have accidentally knocked the sensor loose. A simple reseat fixes it.