March 15, 2026

LG air conditioners with inverter compressor technology are specifically engineered to modulate their output rather than switching abruptly on and off. Because of this design, an LG inverter unit running for extended periods is often normal, especially during the initial pull-down phase when the room is significantly warmer than the set point. Understanding the difference between a correctly operating inverter system and a unit that has developed a genuine fault is the starting point for any diagnosis.

That said, even an LG inverter unit should not run at full compressor output indefinitely once the room has been cooled. When the set temperature has been reached and held but the unit never reduces its output or cycles off entirely, a problem exists. This guide identifies every cause of a continuously running LG air conditioner, from the most common and easily corrected to the component-level repairs that require deeper investigation.

LG Inverter AC: What Continuous Running Actually Means

Unlike fixed-speed compressors that switch fully on or off, LG dual inverter compressors continuously vary their speed between a minimum and maximum frequency to match the actual cooling demand of the room. In practice this means an LG inverter unit may run at low power for hours at a time while maintaining a steady room temperature. This is not a fault and is one of the primary reasons LG inverter units are more energy efficient than non-inverter models.

The fault condition this guide addresses is different: the compressor is running at high or sustained power, the room is not approaching the set temperature, and the unit does not reduce speed or cycle off even after extended operation. This indicates the system is unable to satisfy the thermostat due to one of the causes described below.

Why Your LG AC Keeps Running Without Reaching the Set Temperature

The following causes are responsible for the majority of LG AC continuous-running complaints, listed from the most frequently encountered to the least common.

• Clogged Dual Filter System: LG split and window units use both a primary mesh filter and a secondary nano-carbon filter or ionizer filter on many models. A blocked primary or secondary filter significantly restricts the airflow the blower can deliver across the evaporator coils, reducing cooling capacity below what the room demands.

• Iced-Over Evaporator Coil: Restricted airflow from dirty filters or low refrigerant causes moisture on the evaporator coil surface to freeze. As the ice layer thickens, the coil surface available for heat exchange shrinks, the unit loses cooling capacity, and the compressor runs continuously to compensate for a problem it is making progressively worse.

• Obstructed Outdoor Unit Fan or Blocked Drain Pan: LG outdoor condenser units require unobstructed airflow to expel heat. Dense vegetation, debris accumulation, or a fence positioned too close to the rear of the unit prevents heat from leaving the refrigerant circuit. The compressor keeps running because heat is being removed from the room but cannot exit the outdoor unit fast enough to complete the cycle.

• Faulty Indoor Pipe Temperature Sensor: LG split systems use a dedicated pipe temperature sensor (distinct from the room air thermistor) attached directly to the indoor coil. If this sensor fails or reads inaccurately, the inverter control board incorrectly calculates how hard the compressor needs to work and may keep running it at high output indefinitely.

• Faulty Room Temperature Thermistor: The return air thermistor monitors room air temperature and tells the control board when the set point has been reached. An out-of-range thermistor reports a higher temperature than actual, causing the board to maintain high compressor output past the point where the room has actually cooled.

• Active Auto Clean or Dry Mode: LG air conditioners include an Auto Clean function that runs the fan after cooling to dry the evaporator coil and prevent mold. If the unit appears to continue running after cooling finishes, it may be executing an Auto Clean cycle, which is normal and not a fault.

• Refrigerant Leak and Undercharge: A loss of refrigerant reduces the heat absorption capacity of the evaporator coil. The compressor can continue operating but cannot transfer sufficient heat to satisfy the thermostat, resulting in continuous running with reduced cooling output.

• Control Board Inverter Drive Fault: The inverter control board governs compressor frequency. A fault on the inverter drive module can cause the board to issue a maximum-speed signal to the compressor continuously, bypassing the modulation logic entirely.

Immediate Steps When Your LG AC Won't Stop Running

Before any diagnostic inspection, take these immediate steps to stop the unit and prepare for troubleshooting.

• Press the Mode button on the remote to switch from Cool mode to Fan Only mode. This stops the compressor immediately while keeping the fan running, allowing the evaporator coil to warm up gradually if it has iced over. Check whether the unit now responds to temperature setpoint changes after 10 minutes in Fan mode.

• Press the Power button on the remote to turn the unit off completely. If the unit does not respond to the remote, use the manual Auto button on the indoor unit body. On most LG models, holding the Auto button for 3 seconds powers the unit off.

• If the unit does not respond to either the remote or the manual button, turn off the dedicated AC circuit breaker at the electrical panel. Wait a full 10 minutes before restoring power. This forces a complete inverter board reset that clears temporary fault states.

• Check the LG ThinQ app if your unit is connected to the LG SmartThinQ Wi-Fi system. The app may show an active error code, operating mode, or scheduled timer that explains the continuous running without requiring physical inspection.

• After the unit has been off for 10 minutes, proceed through the diagnostic steps below before restarting.

Fix 1: Clean Both Filter Layers

LG split system and window units often have two filter layers, and both must be clean for full airflow. Many owners clean only the visible outer mesh and overlook the inner secondary filter, which accumulates fine particles that pass through the primary mesh.

1. Power the unit off and open the front panel by lifting it upward.

2. Remove the primary mesh filter from its track by sliding it downward.

3. On models equipped with a secondary filter (nano-carbon, ionizer, or vitamin C filter), remove it from behind the primary filter. Its location and attachment method varies by model but it typically clips into a separate inner frame.

4. Rinse both filters under warm water. The primary mesh can be brushed gently with mild soap. The secondary filter should be rinsed only, without scrubbing, as aggressive cleaning damages the active filter media.

5. Allow both filters to dry fully in a shaded, ventilated area before reinstalling. Reinstalling a damp filter causes frost to form on the evaporator coil.

6. Reinstall the secondary filter first, then the primary mesh. Close the front panel and restart in Cool mode. Allow one complete cooling cycle to confirm the unit now cycles down or reaches the set temperature.

Fix 2: Thaw a Frozen Evaporator Coil

A frozen evaporator coil on an LG unit is easy to identify by a specific symptom pattern: the indoor unit blows air but it is not as cold as expected, water may be dripping from the front grille area, or the front panel feels unusually cold to the touch even with the fan running.

1. Switch the LG unit from Cool mode to Fan Only mode using the Mode button on the remote. Do not attempt to cool the room while the coil is frozen.

2. Set the fan to High speed to circulate maximum airflow over the frozen coil surface.

3. Allow the unit to run in Fan Only mode for 20 to 40 minutes, or until water has stopped dripping from the unit and the airflow from the vents feels room-temperature warm.

4. Open the front panel after the thaw is complete and shine a flashlight at the evaporator coil. The fins should be visible and clear with no white or grey ice coating.

5. Clean the primary and secondary filters before switching back to Cool mode. A clogged filter is the most common cause of coil icing and must be addressed before the problem recurs.

6. If the coil refreezes within two to three days after a thorough thaw with clean filters, a refrigerant leak is the most likely cause. Contact an LG-authorized technician for a refrigerant circuit inspection.

Fix 3: Check the LG Auto Clean and Dry Mode Functions

LG air conditioners include several post-cooling functions that cause the fan to continue running after the compressor stops. These are not faults but can appear to be continuous running if the user is unfamiliar with them.

• Auto Clean: Runs the fan at high speed for 15 to 30 minutes after cooling ends to dry the evaporator coil and prevent mold and mildew from forming on the wet fin surface. The Auto Clean indicator light on the indoor unit face will be illuminated during this phase.

• Fan Auto-Dry Function: On some models, the fan continues briefly after every cooling cycle at low speed to prevent condensate from sitting on the coil surface. This cycle typically lasts 2 to 5 minutes and is not user-controllable.

• Smart Inverter Auto Mode: In Auto mode, the LG inverter determines both temperature and fan speed automatically and may run at low compressor output for extended periods. This can appear to be nonstop running but the compressor output is reduced, not sustained at high output.

To confirm whether one of these modes is active, press the Auto Clean button on the remote to toggle it off. If the fan stops shortly afterward, the unit was executing an Auto Clean cycle and is functioning correctly. If the fan and compressor continue running after disabling Auto Clean, proceed to the sensor and component checks below.

Fix 4: Test the Indoor Pipe Temperature Sensor

The pipe temperature sensor on an LG split system is clipped directly onto the indoor coil pipe and monitors refrigerant temperature inside the coil. The inverter control board uses this reading to determine whether the refrigerant is absorbing heat correctly. A failed pipe sensor that reads a higher temperature than actual causes the board to interpret the coil as insufficiently cold and drives the compressor at maximum output continuously.

1. Turn the unit off and unplug it or switch off the circuit breaker before accessing internal components.

2. Open the indoor unit front panel and remove the filters. The pipe temperature sensor is a small probe, typically white or cream colored, clipped onto the copper refrigerant pipe or pressed against the coil body. It connects to the control board via a two-wire harness.

3. Disconnect the sensor harness connector from the control board.

4. Set a multimeter to resistance (ohms) mode. At room temperature of 68 to 77 degrees Fahrenheit (20 to 25 degrees Celsius), the LG pipe temperature sensor typically reads between 8 and 15 kilohms. A reading significantly outside this range, or an open circuit reading of OL, confirms sensor failure.

5. Replace the pipe sensor with an OEM part specific to your LG model number. The sensor is secured by a simple clip and the harness uses a friction-fit connector, making this a quick replacement.

Fix 5: Test the Room Air Thermistor

The room air thermistor on an LG split system is a small bead sensor positioned in the return air path of the indoor unit, measuring the temperature of the air drawn back into the unit. If this sensor reads above the actual room temperature, the control board keeps the compressor running because it believes the set point has not been reached.

1. Access the indoor unit and locate the room air thermistor. It is typically a small plastic-sheathed bead clipped near the top of the evaporator coil area or in the air intake path, connected by a two-wire harness.

2. Disconnect the harness and test the thermistor with a multimeter set to resistance mode. At room temperature the LG room air thermistor reads approximately 10 kilohms. A reading significantly above 20 kilohms or below 4 kilohms at room temperature indicates a failed sensor.

3. Compare the thermistor reading against the actual room temperature measured by an accurate standalone thermometer placed near the unit's air intake. If the reading corresponds to a temperature significantly higher than the thermometer shows, the thermistor is reporting inaccurately and must be replaced.

4. Replace with an OEM LG thermistor matched to your model. Thermistors are inexpensive parts and are available as a pair (room air plus pipe sensor) for most LG models, making it practical to replace both at the same time since they wear on a similar timeline.

Fix 6: Inspect the Outdoor Unit for Airflow Blockages

LG outdoor condenser units need clear airflow to expel heat efficiently. Unlike some competitors, LG outdoor units for multi-split systems can be mounted in tighter spaces, but single-split units still require minimum clearances. A fully blocked condenser forces the compressor to run continuously as the refrigerant cannot complete the heat rejection half of its cycle.

1. Turn the entire system off before inspecting the outdoor unit.

2. Check the minimum clearances around the unit. The LG installation specification typically requires 12 inches of clear space on the front and sides and 20 inches above the top discharge grille. Measure the actual clearance and remove any vegetation, storage items, or fencing that is encroaching on these zones.

3. Inspect the condenser coil fins visible through the side and rear grilles for dirt, cottonwood fluff, leaf debris, or grass cuttings pressed into the fins. Even a light coating of fine debris across the full fin area significantly reduces heat transfer.

4. Use a soft brush or low-pressure garden hose to clean the condenser fins by directing water from the inside of the unit outward through the fins if the top grille can be removed. This pushes debris out through the same side it entered from. Directing water inward packs debris deeper into the fins.

5. Inspect the condenser fan blade at the top of the unit for damage, debris, or ice. Confirm it spins freely by hand with the unit unplugged. Restart the system and listen for any change in outdoor unit noise after cleaning.

Fix 7: LG Inverter Control Board Diagnosis

If both temperature sensors test within specification, the filters and coils are clean, the outdoor unit is clear, and the refrigerant level has been confirmed correct by a technician but the unit still runs without modulating or cycling off, the inverter drive module on the control board is the final component to investigate. LG inverter boards that develop a fault in the drive circuit issue a maximum-frequency signal to the compressor and lock it into continuous full-speed operation.

1. Turn the unit off, disconnect power, and wait 10 minutes before accessing the control board.

2. On LG split system indoor units, the control board is located in the electrical compartment at the right side of the indoor unit, accessible after removing the front panel, filters, and right-side cover panel.

3. Inspect the board for burn marks or darkening around the inverter drive section, swollen capacitors, or corrosion on terminal connectors.

4. Check whether the LG ThinQ app or any connected diagnostic device is reporting an inverter-related error code before concluding the board has failed. LG error codes beginning with Ch or C (such as Ch 02, Ch 05, or Ch 21) typically indicate compressor or inverter circuit faults.

5. Replace the control board with a genuine OEM LG board matched to your model number. LG board replacements require that the new board is initialized correctly for the specific model. Follow the initialization procedure in the service manual before restarting the unit.

LG AC Error Codes Associated With Continuous Running

LG air conditioners display error codes on the indoor unit display or report them through the LG ThinQ app when a fault is detected. Use these codes to identify the specific component before disassembling the unit.

Diagnostic Summary: Where to Start Based on What You Observe

Cross-reference your specific situation against these symptom patterns to identify your starting point.

• Unit runs constantly and room barely cools after hours of operation: Start with both filter layers, then check for ice on the evaporator coil. Low refrigerant is a strong candidate if filters are clean and no ice is present.

• Unit runs constantly but room has reached set temperature: The room air thermistor is likely reporting a higher temperature than actual. Test thermistor resistance.

• Fan continues running after compressor stops: Check whether Auto Clean mode is active. If the Auto Clean indicator is lit, this is normal operation.

• Unit runs at full blast without modulating speed: On inverter models this indicates an inverter board fault or a pipe temperature sensor failure. Check both.

• Error code displayed on indoor unit or LG ThinQ app: Use the error code section above to identify the indicated component directly.

• Outdoor unit is hot to the touch after extended operation: Condenser coil is dirty or the outdoor unit is obstructed. Clean the outdoor unit fins and check clearances.

Keeping Your LG AC Running Efficiently: Maintenance Schedule

• Clean the primary mesh filter every two weeks during active use. LG units display a filter reminder indicator on the indoor unit.

• Clean the secondary nano-carbon or ionizer filter according to LG's recommendation for your model, typically every 30 days during active use and replacement every 6 months.

• Clean the outdoor condenser unit at the start of each cooling season and again at mid-season in areas with heavy cottonwood, pollen, or dust.

• Use the LG ThinQ app if available to monitor energy consumption patterns. A sudden increase in daily energy use without a change in usage habits often indicates an efficiency problem weeks before continuous running becomes noticeable.

• Have the refrigerant circuit inspected every two years by an LG-authorized technician, particularly if the unit is over five years old.

• Do not set the temperature lower than 65 degrees Fahrenheit (18 degrees Celsius). LG inverter units operating at very low set points work at maximum output for extended periods, accelerating wear on the compressor.