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HomeRepair HelpLennox A/C RepairLennox A/C is short cycling Repair

Lennox Air Conditioner is short cycling

If your Lennox air conditioner is short cycling, or the AC turns on and off quickly before the room reaches the set temperature, the problem is usually in the controls that tell the unit when to run. The most likely cause is a failed control board, followed by the main control board, since either board can send incorrect voltage to the fan, compressor, or other components and make the air conditioner keep cycling. A faulty user control and display board can also cause short run times, especially if the settings respond erratically or the board is not reading sensor input correctly. From there, check the thermistor and temperature sensor, which detect air temperature and should show changing resistance as temperature changes. A bad temperature control thermostat can also short cycle the unit by shutting the compressor off too soon, without allowing the normal five to ten minute pressure equalization delay. Enter your Lennox model number on RepairClinic.com to find the exact replacement control board, thermistor, sensor, or thermostat for your specific air conditioner.

01 - Lennox Air Conditioner Control Board

The control board regulates the voltage to all of the air conditioner components. If the control board fails, the air conditioner may short cycle. Control boards are often misdiagnosed; make sure to check more commonly defective parts first before replacing the control board.
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Highly Likely

02 - Lennox Air Conditioner Main Control Board

The main control board regulates the voltage to all of the air conditioner components. If the control board fails, the air conditioner may short cycle. Control boards are often misdiagnosed; make sure to check more commonly defective parts first before replacing the main control board.
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Highly Likely

03 - Lennox Air Conditioner User Control and Display Board

The user control and display board allows the user to operate the unit by selecting fan speeds and cooling temperatures. If the board is defective, the air conditioner may short cycle. If the temperature sensor or thermistor tests appropriately with a multimeter, it's possible the user control and display board is malfunctioning and will need to be replaced.
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Highly Likely

04 - Lennox Air Conditioner Thermistor

The thermistor is a sensor connected to the control board that detects the temperature of the air. The resistance value of the thermistor changes in conjunction with the air temperature. If the air temperature rises, the resistance value will decrease. A malfunctioning thermistor may cause the air conditioner to short cycle. To determine if the thermistor is at fault, use a multimeter to test it for continuity. If the thermistor does not have continuity, or if the resistance of the thermistor does not change with a change in temperature, replace the thermistor. (To find specific temperature and resistance values, try check...ing your user’s manual.)
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Common

05 - Lennox Air Conditioner Temperature Sensor

The temperature sensor is connected to the control board and detects the temperature of the air. The resistance value of the sensor changes in conjunction with the air temperature. If the air temperature rises, the resistance value will decrease. A malfunctioning temperature sensor may cause the air conditioner to short cycle. To determine if the sensor is at fault, use a multimeter to test it for continuity. If the sensor does not have continuity, or if the resistance of the sensor does not change with a change in temperature, replace the component. (To find specific temperature and resistance values, try checking your us...er’s manual.)
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Common

06 - Lennox Air Conditioner Temperature Control Thermostat

The temperature control thermostat is a sensor which monitors the temperature of the air and activates a switch to provide power to the fan and compressor when the air temperature drops below a set point. If the thermostat isn’t working, the air conditioner may short cycle. When the thermostat shuts the compressor off there needs to be approximately a five to ten minute delay to let the refrigerant equalize before the compressor will start again. If the refrigerant has not had time to equalize the compressor may not start. If the thermostat is short cycling it will need to be replaced. To determine if the temperature contr...ol thermostat is defective, use a multimeter to test it for continuity. If the thermostat does not have continuity, replace it. (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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Common

Frequently Asked Questions

Why is my Lennox air conditioner short cycling?
How do I test a Lennox AC thermistor or temperature sensor?
Can a bad temperature control thermostat make my air conditioner keep cycling?
Should I replace the control board if my Lennox AC turns on and off quickly?
How do I find the right replacement part for my Lennox air conditioner?

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