An intermittent blower motor is a common issue in HVAC systems and vehicles where the fan sporadically stops working, fluctuates in speed, or cuts out entirely. It is most frequently caused by a failing blower motor, a burnt-out resistor, or a bad relay or capacitor.
A faulty resistor or relay can indeed cause the blower motor to stop working or malfunction. "If it only works on high your blower resistor went bad." "The resistor controls how much voltage goes to blower motor. Different fan speeds are different amounts of resistance in the current."
To quickly pinpoint whether the issue is the blower motor or the resistor, check the fan speeds. If the motor only works on the highest setting, or behaves erratically, the resistor is likely bad. If the motor does not work on any speed, the blower motor itself may be failing.
A blower motor constantly turning on and off (short cycling) is usually caused by restricted airflow, a failing motor capacitor, overheating, or a bad control board. This strains your system and should be addressed quickly to prevent permanent damage.
Common causes include dirty or clogged vents and problems with the draft inducer fan. A faulty pressure switch might cause your furnace to turn on and off irregularly or stop after a few minutes. Fixing this often means cleaning vents or replacing the switch.
Resetting a blower motor typically involves cycling the power, checking for tripped thermal switches, or adjusting your thermostat. These methods apply to residential HVAC systems, though the exact steps vary depending on whether you are working on a furnace, an AC unit, or a car's blower motor.
The Furnace Won't Ignite: This is the most common and most telling sign. If the gas valve doesn't open, the ignition sequence simply can't begin. Intermittent Heating or Sudden Shutdowns: These unpredictable cycles often point to weak solenoid coils or unstable electrical connections.
To fix a furnace that is short cycling (turning on and off rapidly without completing a full heating cycle), first replace your clogged air filter, check that all room registers are open, and ensure the outdoor exhaust vent is clear of debris.
How do you know if your furnace blower motor is bad
The $5,000 rule is a guideline to help homeowners decide whether to repair or replace their HVAC system. You multiply the age of your unit by the cost of the needed repair. If that number exceeds $5,000, replacing your HVAC system is often more cost-effective.
A bad blower motor relay will typically cause your HVAC system to produce no airflow, blow warm air only, or leave the fan running constantly. It often fails due to overheated electrical contacts or melted wiring.
The blower motor resistor can be removed after the bolts have been removed. The wire should be linked to the blower motor's positive terminal, and the negative terminal should be attached to the blower motor's negative terminal. This will turn off the resistor and allow the blower motor to run at full speed.
Diagnosing a faulty blower motor versus a bad resistor typically comes down to what fan speeds are working. If the fan only works on the highest setting, the resistor is usually the culprit. If the fan doesn't work on any speed, or if it makes strange noises, the motor itself is likely failing.
Most furnaces have a reset button near the blower compartment itself, though the exact location may vary depending on the make and model. It's usually red or yellow and small in size. Consult your furnace manual for guidance if you're unsure where it is.
The average cost for a Blower Motor Relay Replacement is between $109 and $133. Labor costs are estimated between $50 and $73 while parts are priced between $59 and $60. This range does not include taxes and fees, and does not factor in your unique location.
To reset a furnace blower motor, turn off power to the furnace using the emergency switch or the circuit breaker. Wait 2-3 minutes, then locate the red or yellow reset button typically found on the blower motor housing. Press it firmly, and restore power.
On average, a furnace blower motor lasts between 10 and 20 years. However, this lifespan can be significantly shortened by a lack of maintenance, specifically if air filters are not changed regularly, causing the motor to overheat and overwork.
Here are the 10 most common AC short-cycling causes that homeowners face.
Several signs can indicate furnace short cycling:
Malfunctioning Blower Motor
While less common, a problem with the blower motor can cause a short-cycling furnace. The blower motor works by pushing air through your heating system and sending it out into your home.
To unstick a propane regulator (often caused by the safety bypass valve tripping), turn off all burner knobs, close the tank valve, disconnect the regulator from the tank for 1–2 minutes to "reset" the pressure, then reconnect and slowly open the tank valve. This process resets the internal mechanism that limits flow.
The heat exchanger is often considered the most costly part of a furnace to repair or replace. It is a critical component that transfers heat from the combustion process to the air that circulates throughout your home. Over time, heat exchangers can crack due to the constant heating and cooling cycles they undergo.
Signs of a failing control board include the furnace not starting, the blower fan running nonstop, flashing error codes on the unit, and the system not responding to the thermostat.