The part(s) or condition(s) listed below for the symptom Air handler not heating 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.
Electric furnaces and air handlers will use a heating element instead of a burner assembly to heat the air that will be circulated through the home. A defective heating element can cause the unit not to heat. Most electric elements require 220 volts and there may be more than one element. You use a multimeter to test all the elements and limit thermostats for electrical continuity, a continuous electrical path present in the components, to help determine if they are defective. The heating element may come as an assembly with limit thermostats included.
The control board regulates the power supply to all of the components of the furnace or air handler. If the control board fails, it might not send voltage to the ignition system, causing the unit not to heat.
The main control board regulates the power supply to all of the components of the furnace or air handler. If the control board fails, it might not send voltage to the ignition system, causing the unit not to heat.
The furnace or air handler thermostat monitors the heat being generated by the unit and will shut off power to the heating circuit if the temperature gets too high. A defective thermostat may not allow the unit to heat the air at all. You can use a multimeter to test the thermostat for electrical continuity, a continuous electrical path present in the component. If the thermostat tests negative for continuity, the part should be replaced.
The limit switch monitors the heat surrounding the heating elements or other heat sources. To determine if the limit switch is defective, use a multimeter to test it for continuity. If the switch does not have continuity and the reset button has not tripped, the limit switch should be replaced. Be aware that poor airflow through the heater will often result in a tripped limit switch. Make sure that the furnace or air handler is in a properly ventilated location, the air filter is clean, and the air vents are clear of obstructions.
The furnace or air handler 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 other heating circuit components. If the contactor is defective, the heating circuit will not receive the voltage needed to operate. 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.
The wall thermostat has electrical contacts that control the power supply to the furnace or air handler. If the contacts in the thermostat fail, the unit will not turn on. To determine if the thermostat is defective, use a multimeter to test it for continuity. If the wall thermostat does not have continuity, replace it.
The WiFi thermostat has electrical contacts that control the power supply to the furnace or air handler. If the contacts in the thermostat fail, the unit will not turn on. To determine if the thermostat is defective, use a multimeter to test it for continuity. If the WiFi thermostat does not have continuity, replace it.
The air handler must have proper airflow through the heating elements or heat pump coils in order to run properly. The air handler draws air from the surrounding area or through the return air duct in the home or building. If the air handler is located in a utility closet or in a cramped storage room, there may not be sufficient available air for the furnace to heat properly. Make sure the air filter is not clogged, It is recommended to replace the air filter at least every 6 months or sooner depending on the conditions.
If the air handler stops working properly the control board will often display a fault code to help diagnose the problem. The fault codes are displayed by a flashing light or multiple lights on the control board. Each sequence of flashes followed by a pause will indicate either an error code or the status of the air handler. Some manufacturers will use red and green lights to indicate specific fault codes. Fault codes are often displayed on the access cover of the air handler for easy reference.
The spinning blower wheel will circulate the heated air throughout the home's venting. If something is obstructing the blower wheel and preventing it from turning, the air won't be circulated. Inspect the blower wheel and housing for any obstructions and confirm the wheel is properly seated on the motor shaft and can rotate freely.
The blower motor spins a blower wheel to circulate the heated air throughout the home's venting. If the motor is burned out, the air will not be circulated. You should try turning the blower wheel by hand to determine if it can rotate freely. If blower wheel does not turn freely, it's likely the blower motor bearings have seized and the motor will need to be replaced. You can also use a multimeter to determine if voltage is reaching the motor. If power is getting to the component, but the motor doesn't run, it is likely defective.
A furnace or air handler transformer is the component that decreases or increases the incoming voltage to power the unit. A faulty transformer can prevent the unit from heating. If there is no secondary 24 volt power to the thermostat, the unit trips a circuit breaker when it comes on, or you hear a consistent humming or vibrating noise, it's possible the transformer has failed.
Check to see if there is power to the air handler. There should be a steady light on the control board. If there is no power to the air handler, check the home's circuit breaker or fuse. Confirm the power switch on the side of the air handler is turned on.
Most wall thermostats are either powered by an enclosed battery or by the air handler control board or 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.
