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Medallion Central air conditioner won't turn off

Won’t your Medallion 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 electrical contacts stick closed, the thermostat keeps sending a signal through the yellow Y thermostat wire to the control board and contactor, making the air conditioner run continuously. With power safely disconnected, a qualified DIYer can test the thermostat for continuity between the common C and yellow Y terminals while the thermostat is set to off. If continuity remains, replace the thermostat. A shorted contactor is less common but can also keep the condensing unit energized even when the thermostat is off. This repair involves low-voltage controls and potentially 240V line voltage, so do not test or replace the contactor, control board, or other energized condensing-unit parts unless you are qualified. Turn off the disconnect box and circuit breaker before inspection, and hire an HVAC technician for line-voltage work. No refrigerant handling is typically needed. Enter your Medallion model number to find the exact replacement control board, thermostat, or contactor for your central air conditioner.

01 - Medallion 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 - Medallion 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 - Medallion 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 - Medallion 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 - Medallion 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 Medallion central air conditioner turn off?
How do I test a thermostat when my AC keeps running?
Can a bad AC contactor cause the air conditioner not to shut off?
Should I replace the Medallion control board if the AC won't turn off?
How do I find the correct Medallion replacement part for an AC that keeps running?

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