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Central air conditioner won't turn off

If your central air won't turn off, the system may be receiving a continuous cooling signal even when the thermostat is set to Off. The most likely cause is a failed furnace control board or main control board with a short that keeps sending voltage to the central air condensing unit. Next, check the wall thermostat or thermostat wiring. Stuck electrical contacts between the common "C" and yellow "Y" thermostat wire terminals can keep the contactor energized, causing the air conditioner to run constantly. A shorted central AC contactor is less common but can also keep the condensing unit powered. These checks can help narrow down why the unit is not operating normally and identify the correct replacement part." You can inspect the thermostat, wiring, and control board for visible damage, but testing or replacing a contactor involves 240V line voltage and should be handled by a qualified HVAC technician unless you are trained and equipped to do it safely. Enter your central air conditioner's model number to find the exact replacement control board, thermostat, or contactor for your system.

01 - Central Air Conditioner Control Board

If the furnace control board has a short, it may be providing continuous voltage to the central air condensing unit preventing it from turning off. Inspect the control board for any damage and replace if necessary.

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Common

02 - Central Air Conditioner Main Control Board

If the furnace's main control board has a short, it may be providing continuous voltage to the central air condensing unit preventing it from turning off. Inspect the control board for any damage and replace if necessary.

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Common

03 - Central Air Conditioner Wall Thermostat

The wall thermostat has electrical contacts that send signal voltage back to the control board and the condensing unit's contactor to run the central air system. If the contact that controls the contactor sticks closed, it will send continuous voltage to the contactor, causing the central air system to run continuously. To determine if the thermostat is defective, use a multi-meter to test it for continuity. If the wall thermostat shows continuity between the common (“C”) and yellow (“Y”) thermostat wire terminals when the thermostat is in the off position, the thermostat has failed and will need to be replaced.

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Common

04 - Central Air Conditioner Wifi Thermostat

The WiFi thermostat has electrical contacts that send signal voltage back to the control board and the condensing unit's contactor to run the central air system. If the contact that controls the contactor sticks closed, it will send continuous voltage to the contactor, causing the central air system to run continuously. To determine if the thermostat is defective, use a multi-meter to test it for continuity. If the WiFi thermostat shows continuity between the common (“C”) and yellow (“Y”) thermostat wire terminals when the thermostat is in the off position, the thermostat has failed and will need to be replaced.

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Common

05 - Central Air Conditioner Contactor

The furnace control board sends a low voltage signal to the contactor. When the contactor receives the signal from the control board, it closes the circuit, sending voltage to the condensing unit components. If the contactor has shorted, it can send continuous voltage to the condensing unit's components resulting in the central air system not turning off. To determine if the contactor is at fault, use a multimeter to test the contactor for a short. If the contactor has shorted, replace it.

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Less Common

Frequently Asked Questions

Why won't my central air conditioner turn off?

Can a wall thermostat cause my AC to keep running constantly?

How do I know if the AC contactor is stuck or shorted?

Could a control board be causing my central air conditioner not to shut off?

How do I identify the correct replacement part for an AC that won't turn off?

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