Mars Central air conditioner won't turn off

If your Mars 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, followed by the main control board, which can short and keep sending voltage to the outdoor condensing unit. Next, check the wall thermostat or thermostat wiring. A stuck contact between the common C and yellow Y thermostat wire terminals can keep the contactor energized and cause the AC to keep running. The contactor itself is less commonly at fault, but a shorted contactor can continuously power the condenser components. This troubleshooting applies when the central air won't turn off, the AC won't shut off, or the air conditioner is running constantly. You can inspect the thermostat and control board for visible damage, but turn off power at the circuit breaker and disconnect box before opening panels. The contactor and other condensing unit components use dangerous 240V line voltage, so have a qualified HVAC technician handle energized testing or replacement. Enter your Mars model number to find the exact control board, thermostat, or contactor replacement part for your central air conditioner.

01 - Mars 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 - Mars 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 - Mars 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 - Mars 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 - Mars 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 Mars central air conditioner turn off?

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

Can a bad AC contactor cause the air conditioner to run constantly?

Should I replace the control board if my Mars central AC won't shut off?

How do I find the correct replacement part for my Mars central air conditioner?

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