Nutone Central air conditioner won't turn off

Won’t your NuTone central air conditioner turn off? A shorted contactor or a bad wall thermostat or thermostat wiring is the most likely cause, keeping a cooling signal on the yellow (Y) terminal even after the thermostat is set to Off. A shorted furnace control board or main control board can cause the same problem, though it is a less common cause, by continuing to send voltage to the outdoor condensing unit and making the air conditioner run constantly. Next, check the wall thermostat or thermostat wiring. If its contacts stick closed, it can continuously send a signal through the C and Y thermostat wire terminals to the control board and contactor. With the thermostat set to Off, a qualified DIYer can use a multimeter to check for continuity between C and Y. If continuity remains, replace the thermostat. A shorted contactor is less common but can also keep the central air from shutting off by supplying continuous power to the condensing unit. Turn off the disconnect box and circuit breaker before inspecting components. Control boards and contactors involve low- and high-voltage circuits, including potentially dangerous 240V power, so use a licensed HVAC technician if you are not trained for line-voltage testing or replacement. Enter your NuTone model number to find the exact control board, thermostat, or contactor for your central air conditioner.

01 - Nutone 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 - Nutone 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 - Nutone 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 - Nutone 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 - Nutone 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 NuTone central air conditioner turn off?

How do I test a thermostat when my central air won't shut off?

Can a bad contactor cause an AC unit to run constantly?

Could the NuTone furnace control board or main control board be keeping the AC on?

How do I find the correct NuTone AC part when the system won't turn off?

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