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Trane Central Air Conditioner Not Cooling

The part(s) or condition(s) listed below for the symptom Central air conditioner not cooling are ordered from most likely to least likely to occur. Check or test each item, starting with the items at the top of the page.

Most Frequent Causes for Central air conditioner not cooling

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Cause 1Main Control Board

If the central air condensing unit contactor is not receiving 24 volts or power is not getting to the furnace blower motor, a possible cause is a defective furnace main control board. While this is not a common problem, if all other potentially faulty components are working properly, the main control board should be replaced.

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Cause 2Air Flow Problem

If the condenser coil is clogged with debris the condenser fan will not be able to remove the heat from the coil, resulting in a loss of cooling. The coil can be cleaned with a garden hose and spray nozzle from the inside out. If the coil is excessively dirty, a coil cleaner spray can be used to help loosen the dirt. If the furnace filter has not been replaced recently it will need to be checked and replaced if needed.

Cause 3Contactor

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 is defective, it will not provide voltage to the condensing unit. To determine if the contactor is at fault, use a multimeter to test the contactor for continuity. If the contactor does not have continuity, replace it.

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Cause 4Dual Run Capacitor

If the dual run capacitor is defective, the fan motor might be noisy, overheat, or not run at all. To determine if the dual run capacitor has failed, inspect the capacitor. If the dual run capacitor is bulging or leaking, replace it.

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Cause 5Sealed System Problem

If the unit has good air flow, the evaporator and condensing unit coils are clean, the fan and compressor are running, and the furnace blower is on, but there is still not enough cooling, it is likely there is a leak or restriction in the sealed system. Since diagnosing and repairing a sealed system takes specialized tools and knowledge, a qualified service technician should diagnosis and repair the unit.

Cause 6Incoming Power Problem

The central air condensing unit is energized with 240 volts of electricity. The electricity flows through a disconnect box to the compressor and condenser fan motor. The disconnect box enables the air conditioning unit to be turned off outside. The disconnect box includes a cartridge which may contain fuses. If the compressor and condenser fan motor do not run, the disconnect box fuses may have blown, or the circuit breaker that supplies power to the disconnect box may have tripped. To determine if the disconnect box fuses have blown, use a multimeter to test the fuses for continuity. If the disconnect box fuses do not have continuity replace them.

Cause 7Thermostat Not Set Properly

For the central air conditioner to work properly the wall thermostat should be set for "Cool" and the fan set for "Auto" or "Fan On". The temperature setting also needs to be set colder than the room temperature. When the thermostat is set properly both the outdoor consensing unit and the furnace blower should be running.

Cause 8Run Capacitor

If the run capacitor is defective, the fan motor might be noisy, overheat, or not run at all. To determine if the run capacitor has failed, inspect the capacitor. If the run capacitor is bulging or leaking, replace it.

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Cause 9Condenser Fan Motor

To determine if the condenser motor is working, use a multimeter to test the incoming voltage to the motor. If the condenser fan motor is receiving the correct voltage but the motor still won’t run, inspect the capacitor to ensure that it is not at fault. If the capacitor is not bulging or leaking, replace the condenser fan motor.

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Cause 10Capacitor

If the capacitor is defective, the fan motor might be noisy, overheat, or not run at all. To determine if the capacitor has failed, inspect the capacitor. If the capacitor is bulging or leaking, replace it.

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Cause 11Compressor

The compressor is a pump which compresses the refrigerant and circulates the refrigerant through the evaporator and condenser coils. If the compressor is not working, the central air conditioner won’t cool. However, this isn’t usually the case. Before replacing the compressor, first check all of the more commonly defective components. If all of the other components are working properly, use a multimeter to test the compressor for continuity. If there is an open circuit, the compressor is likely defective. If the compressor is defective, it must be replaced by a licensed technician.

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Cause 12Control Board

If the central air condensing unit contactor is not receiving 24 volts or power is not getting to the furnace blower motor, a possible cause is a defective furnace control board. While this is not a common problem, if all other potentially faulty components are working properly, the control board should be replaced.

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Cause 13Blower Motor

Since the furnace's blower motor is the component that circulates the cooled air through the home's venting, a defective blower motor will result in the central air conditioner not cooling. You can use a multimeter to test the blower motor for electrical continuity, a continuous electrical path present in the motor, as well as determine if power is reaching the motor. You can also try turning the blower wheel by hand. If the wheel does not turn freely, it's likely the motor bearings have seized and the blower motor will need to be replaced.

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Cause 14Motor

Since the furnace's circulation blower fan motor is the component that circulates the cooled air through the home's venting, a defective motor will result in the central air conditioner not cooling. You can use a multimeter to test the motor for electrical continuity, a continuous electrical path present in the motor, as well as determine if power is reaching the motor. You can also try turning the blower wheel by hand. If the wheel does not turn freely, it's likely the motor bearings have seized and the motor will need to be replaced.

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Cause 15Transformer

The furnace control board sends a low voltage signal of 24 volts to the contactor. When the contactor receives the signal from the control board, it closes the circuit, sending voltage to the condensing unit components. Some furnaces have a separate transformer for the 24 volt circuit, so if the contactor is not receiving the proper voltage, it's likely this transformer has failed and the component will need to be replaced.

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Cause 16Wall Thermostat

The furnace control board sends a low voltage signal of 24 volts to the contactor through the wall thermostat. When the contactor receives the signal from the control board, it closes the circuit, sending voltage to the condensing unit components. There should be 24 volts between the common (“C”) and yellow (“Y”) thermostat wire terminals on the furnace control board when the wall thermostat is in the cooling mode. You can check for this voltage with a multimeter. If voltage is not reaching the contactor, it's likely the wall thermostat is defective and will need to be replaced.

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Cause 17Wifi Thermostat

The furnace control board sends a low voltage signal of 24 volts to the contactor through the WiFi thermostat. When the contactor receives the signal from the WiFi thermostat, it closes the circuit, sending voltage to the condensing unit components. There should be 24 volts between the common (“C”) and yellow (“Y”) thermostat wire terminals on the furnace control board when the WiFi thermostat is in the cooling mode. You can check for this voltage with a multimeter. If voltage is not reaching the contactor, it's likely the WiFi thermostat is defective and will need to be replaced.

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