LG Window AC CH05 Error Code — Condenser Thermistor Fault

Your LG window air conditioner is displaying CH05, which means the condenser coil temperature sensor (a secondary thermistor) has failed or is reading out of range. While CH01 tracks the room air temperature, CH05 tracks the temperature of the outdoor coils — the condenser.

When this sensor fails, the control board doesn’t know if the condenser is at a safe operating temperature. It shuts down the compressor as a safety precaution. The unit may run the fan but won’t produce cold air.

This is slightly more involved than the CH01 fix because the condenser thermistor is located near the hot, dirty outdoor section of the unit. But with the right approach, you can still fix it yourself.

Quick Reference

Fix 1: Check for a Dirty Condenser Coil

Before blaming the sensor, take a good look at the condenser coils (the outdoor fins on the back of the window AC). A blocked or heavily dirty condenser can overheat and trip the CH05 code even if the sensor itself is fine. The control board sees a temperature that’s too high and flags it as a sensor fault.

1. Unplug the unit from the wall.
2. Pull the AC forward so you can see the back (outdoor side).
3. Inspect the condenser fins — look for dirt, dust, lint, pet hair, or debris packed between the metal fins.
4. Check for bent fins — smashed fins from rough handling or installation can restrict airflow.

If the coils are dirty, move to Fix 2. If they’re clean, skip to Fix 3.

Fix 2: Clean the Condenser Coils

A thorough coil cleaning often clears CH05. This is basic maintenance every window AC needs anyway.

1. Brush off loose debris with a soft brush or vacuum with a brush attachment.
2. Spray on coil cleaner — use a dedicated AC coil cleaning spray. Let it sit for 10 minutes as the label directs.
3. Rinse gently — carefully rinse from the outside in. Don’t blast water into the unit.
4. Straighten bent fins — use a fin comb to straighten any crushed fins for better airflow.
5. Let it dry completely — wait at least a few hours before plugging back in.

Once dry, plug in and test. If CH05 is gone, you just needed a spring cleaning. If not, the thermistor itself is likely bad.

Fix 3: Test the Condenser Thermistor

If cleaning didn’t help, it’s time to test the sensor. You’ll need a multimeter.

1. Unplug the AC.
2. Remove the front grille and the top housing cover to expose the control board area.
3. Find the condenser thermistor — it’s different from the room thermistor on the front. The condenser thermistor is clipped into the condenser coil fins (the outdoor section). It may have two wires running to a separate connector on the control board labeled “COND” or “COIL.”
4. Disconnect the thermistor from the control board.
5. Set your multimeter to ohms (Ω).
6. Test the thermistor at room temperature — for an LG window AC condenser thermistor, expect roughly 10kΩ at 77°F. This is the same 10k NTC type used in many LG window ACs, though some models use 5kΩ or other values.

If you get OL (open loop), 0Ω, or a fixed reading that doesn’t change when you warm the bead with your fingers, the thermistor is bad.

Fix 4: Replace the Condenser Thermistor

If the test confirms a bad sensor, replacement is the fix.

1. Order a compatible thermistor. An LG window AC condenser thermistor works for most models. Double-check that the connector type and resistance value match your unit.
2. Unplug the unit (still unplugged, hopefully).
3. Remove the old thermistor from its clip on the condenser coil. You may need to unwrap it from the copper tubing if it’s strapped on.
4. Disconnect the wires from the control board.
5. Route the new sensor wire along the same path and plug it into the correct connector on the board (COND or COIL).
6. Clip the new thermistor into the same position on the condenser coil. It needs good thermal contact with the coil fins.
7. Reassemble the housing and grille.
8. Plug in and test. Run the unit in Cool mode for 20 minutes.

If the compressor kicks on and stays on, the fix worked.

Fix 5: Replace the Control Board (Unlikely, But Possible)

If you’ve cleaned the coils and replaced the thermistor but CH05 persists, the sensor circuit on the control board may be damaged. This is rare with LG window ACs but possible after a power surge.

1. Find a compatible LG AC control board.
2. Disconnect power and remove the control panel.
3. Take photos of every wire connection.
4. Swap in the new board and reconnect everything.
5. Test.

Given that a replacement window AC costs $150–$500, a control board swap only makes financial sense on larger units. If your AC is a small model (under 8,000 BTU), do the math before buying.

Parts You Might Need

• LG window AC condenser thermistor (10kΩ compatible)
• AC coil cleaning spray
• Fin comb for condenser fins
• Digital multimeter
• Universal AC control board

Preventing CH05 in the Future

CH05 is often a maintenance code in disguise. A clean condenser coil runs cooler, and a cooler coil puts less stress on the thermistor and compressor.

• Clean the coils once a year, ideally at the start of cooling season.
• Keep debris away from the outdoor side of the window AC. Trim bushes or leaves that block airflow.
• Check the fins after each installation. Smashing a unit into a window frame can bend fins.
• Use a cover in the off-season to keep dust and debris out of the condenser area.

Related Guides

• LG Window AC CH01 Error Code — Room Thermistor Fault
• LG Window AC Error Codes — Complete Guide
• All LG Appliance Resources