Warning!! blowers can cause injury if you do not turn the power off! Additionally, blowers that are belt driven can be harmful to loose clothing and fingers. Be very cautious when working around moving parts such as blowers.

Air Handler Blower MotorAir Handler Blower Motor - All air handling units have a blower located inside the air handler cabinet. The air handler blower motor has a motor that drives it. Some air handling unit blowers are direct drive and some are belt driven. Many light commercial and residential blowers are direct drive blower motors by the motor’s shaft while many commercial air handling units are belt driven by the blower motor and some sheaves attached to the blower motor shaft and the shaft attached to the blower wheel. Some sheaves are adjustable and some are not. If the belt is slipping always change the belt first before adjusting the sheave. Adjusting the sheave can cause the unit to produce more or less than designed airflow. Sheaves are typically set by Testing and Balancing HVAC Technicians.

Some motors require regular maintenance in the form of oil or grease. All these air handling unit blower motors, whether they are commercial or residential, have high voltage running to them which can be potentially dangerous. The other danger involved with checking these air handler blower motors is they are moving parts when energized and can cause serious injury. It is recommended in commercial applications to replace the belts at least every ninety days. A qualified HVAC technician should perform this as routine air handler maintenance. While this is done bearings and other parts should be checked for unusual wear and lubricated as necessary.

Air Handler Blower Motor - Preventive Maintenance

Regular motor preventive maintenance is necessary for the air handler blower especially if it is belt driven as belts wear out and need to be replaced or the belt will break or begin slipping and you will lose efficiency. It is also important that the sheaves be checked for unusual wear as the blower sheaves also wear over time and need to be replaced. It is not uncommon to have adjustable sheaves on many belt drive blowers and blower motors.

It is important that the adjustments on these sheaves not be changed except by a qualified air balancing technician. The sheaves are adjusted at the time of balancing by a qualified balancing firm and are adjusted according to the engineers’ calculations of air flow for the zone or zones being served by the air handling unit. Blowers can also accumulate dust and the duct will reduce efficiency so it is necessary from time to time to clean the blower including the blower vanes just as one would clean the air handler evaporator coils from to time.

Air Handler Blower Motor - Basic Checks

air handler blower sheavesSome blower motors require regular maintenance while other blower motors do not require regular maintenance. Blower motor maintenance includes a basic check of electrical connections and controls for the blower motor and periodic lubrication of the bearings. Lubrication maintenance will also include lubrication maintenance of blower shaft bearings if the unit is belt driven.

It is important that all safety precautions be used when performing any type of maintenance on any type of mechanical equipment. Some blowers have sealed bearings and these motors do not require periodic lubrication. Always check with the motor manufacturer or a qualified motor representative for proper motor maintenance.

Air Handler Blower Motor - Alignment is Critical

One other word of note about air handler blower maintenance is the alignment of the blower motor. If a particular air handler blower that is belt drive consistently wears out belts more than average the alignment between the blower sheave and the motor sheave needs to be looked at. Sheaves that are not aligned with blower motors and blowers will cause abnormal wear of belts and sheaves and cause nuisance breakdowns especially breaking the belts and slipping belts eventually leading to failure.

The tension of the belt is also important. If the belt is too tight it will cause abnormal bearing wear and possibly bearing failure. If the belt to lose the belts will slip and wear prematurely. A special tool can be used for proper belt tension and is usually available from your local HVAC supply warehouse. A special is also available for aligning the sheaves between the blower and the motor sheaves.


All air handling units have a blower located inside the air handler cabinet. The air handler blower has a motor that drives it. Some air handling unit blowers are direct drive and some are belt driven. Many light commercial and residential blowers are direct driven.

Lastly, other Resources to help you with Capacitors and HVAC Motors:

High Performance HVAC

The Air Handler Blower

To learn more about heating systems and HVAC use this resource.

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