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HomeRepair HelpCarrier Central A/C RepairCarrier Central air conditioner won't turn on Repair
Carrier Central air conditioner won't turn on
When your Carrier central air conditioner won't turn on, the most likely cause is a failed transformer. The transformer supplies the 24-volt signal that allows the thermostat to energize the contactor and start the condensing unit. A defective furnace control board is another highly likely cause, especially if the contactor is not receiving 24 volts or the furnace blower motor has no power. If the thermostat display is blank, replace its batteries, then check for an incoming power problem, such as a tripped circuit breaker, blown fuse, or furnace or air handler power switch that is turned off. Less common causes include a defective wall thermostat, thermostat wire, or wall thermostat that is not sending the cooling signal. You can safely replace thermostat batteries and inspect accessible switches, but testing or replacing a transformer, control board, contactor, or other component may involve 240-volt line voltage. Turn off power before servicing, and have a qualified technician handle live-voltage diagnosis. This symptom does not usually require refrigerant work, but any sealed-system repair requires an EPA 608-certified HVAC technician. Enter your Carrier model number to find the exact replacement part for your central air conditioner.
01 - Carrier Central Air Conditioner Transformer
The furnace control board sends a low voltage signal of 24 volts to the thermostat. When the themostat cooling contacts close, a 24 volt signal is sent to the contactor coil, closing the high voltage circuit and sending power 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 when the thermostat cooling contacts are closed, it's likely this transformer has failed and the component will need to be replaced.
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Highly Likely
02 - Carrier Central Air Conditioner 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 control board. While this is not a common problem, if all other potentially faulty components are working properly, the control board should be replaced.
Highly Likely
03 - Wall Thermostat Batteries
Most wall thermostats are either powered by an enclosed battery or by the furnace or air handler transformer. If the thermostat display is dead, you can remove the thermostat cover and look for replaceable batteries. Replace the batteries if needed and check operation.
Common
04 - Incoming Power Problem
Check to see if there is power to the furnace or air handler. One or more indicator lights on the control board should be illuminated. If there is no power to the furnace or air handler, check to see if a circuit breaker has tripped or a fuse has blown. Confirm the power switch on the side of the unit is turned on.
Common
05 - Carrier Central Air Conditioner Wall 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 wall 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 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.
Less Common
06 - Carrier Central Air Conditioner Wifi 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.
Less Common
Frequently Asked Questions
Why is my Carrier central air conditioner not turning on?
How do I know if my AC thermostat is not turning on the air conditioner?
What should I check when the outdoor AC unit is not turning on but the thermostat works?
Could a failed transformer or control board keep my Carrier AC from starting?
How do I find and buy the correct Carrier central air conditioner replacement part?
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