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Carrier Central air conditioner won't turn off

If your Carrier central air conditioner won't turn off, the system may be receiving a continuous run signal even when the thermostat is set to Off. The most likely cause is a failed furnace control board, which can short and keep sending voltage to the outdoor condensing unit. A faulty main control board can cause the same problem. 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 continuously. Less commonly, the condensing unit contactor may be shorted and continue supplying power to the compressor and condenser fan motor. Turn off power at the disconnect box and circuit breaker before inspecting wiring or parts. Thermostat replacement and basic visual checks may be suitable for a careful DIYer, but control board and contactor testing or replacement involves low-voltage controls and potentially dangerous 240V line voltage, so use a qualified HVAC technician if you are not trained for this work. Enter your Carrier model number to find the exact replacement control board, thermostat, or contactor for your central air conditioner.

01 - Carrier 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 - Carrier 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 - Carrier 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 - Carrier 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 - Carrier 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 Carrier air conditioner turn off?
How do I know if my Carrier thermostat is causing the AC to run constantly?
Can a stuck contactor make a Carrier AC unit run continuously?
Should I replace the Carrier control board if my air conditioner won't turn off?
How do I find the correct Carrier AC part when the unit won't shut off?

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