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HomeRepair HelpLennox A/C RepairLennox Air conditioner won't turn off Repair
Lennox Air conditioner won't turn off
If your Lennox air conditioner won’t turn off, start with the parts and conditions most likely to make the AC run continuously. Dirty condenser coils are the top suspect because built-up debris keeps the unit from releasing heat, which can make the compressor keep running while it tries to reach the set temperature. Next, check the temperature control thermostat, since a shorted thermostat can send constant voltage to the fan motor and compressor. A defective thermostat can cause the same problem if it does not properly sense or switch with room temperature. A dirty or damaged air filter can also reduce airflow and cooling capacity, making the air conditioner keep running longer than normal. Less commonly, a failed thermistor may misread room temperature and keep the compressor running constantly, or a faulty relay board may continue sending voltage to the compressor. Use your wiring diagram and a multimeter where needed, and enter your Lennox model number on RepairClinic.com to find the exact replacement thermostat, thermistor, relay board, air filter, or other part that fits your specific air conditioner.
01 - Condenser Coils are Dirty
The condenser coils dissipate the heat as the refrigerant passes through the coils. If the condenser coils are dirty, they won’t be able to dissipate the heat as effectively. As debris builds up on the coils, the air conditioner will become less efficient, causing the air conditioner to work harder to cool down. If the coils are significantly dirty, the air conditioner will not be able to maintain the proper temperature, and the compressor will run continuously in an attempt to cool the room. Check the condenser coils to determine if they are dirty. Refer to owner's manual for cleaning instructions.
Top Solution
02 - Lennox Air Conditioner Temperature Control Thermostat
The temperature control thermostat provides voltage to the fan motor and compressor. If the thermostat has shorted out, it might send continuous voltage to the compressor and cause the compressor to run all the time. To determine if the thermostat is shorted out, use a multimeter to test it for continuity. If the thermostat has continuity all the time, this indicates that it is shorted out and should be replaced. (Note: Some thermostats may also control a heater and, as a result, will have three terminals. Refer to your air conditioner’s wiring diagram for more information.)
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Highly Likely
03 - Lennox Air Conditioner Thermostat
The thermostat monitors the temperature of the air. When the air temperature rises above a set point, the thermostat activates a switch to provide power to the fan and compressor. If the thermostat is defective, it may cause the compressor to run continuously. To determine if the thermostat is defective, set the air conditioner to cooling and then use a multimeter to test the thermostat for continuity. If the thermostat does not have continuity while the air conditioner is set to cooling, replace the thermostat. (Note: Some thermostats may also control a heater and, as a result, will have three terminals. Refer to your air...
Highly Likely
04 - Dirty or Damaged Air Filter
A dirty air filter will greatly reduce the cooling capacity of the air conditioner, which may cause the unit to run longer than normal. Most air filters used in stand-alone air conditioners can be cleaned with soap and water. Only filters that are extremely clogged with debris or damaged will need to be replaced. Refer to owner's manual for guidance.
Common
05 - Lennox Air Conditioner Thermistor
The thermistor is a sensor which detects the room air temperature. It is connected to the control board. If the thermistor is defective it will not have continuity when it should. If this happens the compressor runs all the time.
Common
06 - Lennox Air Conditioner Relay Board
The relay board provides voltage to many of the air conditioner components, including the fan motor and compressor. If there is a problem with the relay board, it might provide continuous voltage to the compressor. However, this is almost never the case. Before you replace the relay board, make sure you check more commonly defective parts. If you are certain that all of the other components are working properly, replace the relay board.
Common
Frequently Asked Questions
Why won't my Lennox air conditioner turn off?
Can dirty condenser coils make my AC run continuously?
How do I test a Lennox air conditioner temperature control thermostat?
Can a bad thermistor cause an air conditioner compressor to run constantly?
How do I find the right Lennox air conditioner part at RepairClinic.com?
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