To determine if your blower motor or its relay is bad, check for airflow at different speeds. A bad relay often causes the fan to stop working entirely or run only on specific speeds. A bad blower motor typically gives physical warning signs like squeaking noises, blowing weak air, or failing intermittently before dying.
A bad blower motor relay acts as a faulty switch, preventing electrical current from reaching the fan. Common symptoms include a blower fan that does not turn on at all, a fan that stays running even when the vehicle is off, weak or inconsistent airflow, or clicking sounds from the dashboard.
Common signs of relay failure include intermittent power loss to connected devices, unresponsive switches, or a constant clicking sound when you try to activate a system. In vehicles, faulty relays frequently cause starting issues, dead fuel pumps, or malfunctioning headlights and cooling fans.
Replacing a blower motor relay typically costs between $𝟏𝟓 and $𝟐𝟎𝟎 total for a car, and $𝟏𝟎𝟎 to $𝟒𝟓𝟎+ for a home HVAC system. The part itself is very affordable, ranging from $𝟏𝟎 to $𝟓𝟎, with the remaining cost driven by labor and diagnostic fees.
Testing a blower motor relay involves a quick "swap test," an audible click test using a 12V battery, and a continuity check using a multimeter. This helps determine if your HVAC issues stem from a faulty relay, a blown fuse, or the blower motor itself.
To check if an electrical relay is bad, you can do a quick swap with an identical working relay, test its internal coil with a multimeter, or energize it with a battery to see if the internal switch clicks.
Resetting a blower motor typically involves safely power-cycling the HVAC system, pressing the motor's physical reset button, or resetting the circuit breaker.
Nearly all of the relays on a car, including the blower motor relay are built to last for as long as the car does.
If your blower motor resistor goes out, your car's heater and air conditioning fan will likely lose its ability to change speeds. The most common symptoms include:
Possible Causes of a Bad Cooling Fan Relay
Damage caused by changing between circuits with different speeds and electrical load. Ants in the relays (more common than you'd expect). Relay failure due to high current draw from a partially shorted fan motor or intermittently shorted fan circuit.
The two most common faults in a relay are contact degradation (or "burning") and coil burnout. These issues result from physical wear and tear caused by frequent switching and electrical stress.
The main symptom you may experience if a relay is failing is a lack of power to one or more systems on your vehicle, but more specifically this could cause issues like: Failure to turn the engine over (starter relay) No fuel pressure and a no-start condition (fuel pump relay)
The method to reset a relay depends entirely on the type of relay you are using:
A fan relay is stuck on if the radiator or HVAC fan continues running long after the engine is turned off, or if it runs constantly even when the system is switched off. This happens when the internal contacts weld together, keeping the circuit permanently closed.
Common relay failure symptoms include unexpected clicking or buzzing sounds, total non-operation of an electrical component, intermittent power loss, and burnt smells or melted plastic housings. Because a relay acts as a switch, its failure generally disrupts power flow to the connected system.
The blower motor relay is typically located either in the main under-hood fuse box or tucked under the passenger-side dashboard near the glove box. In many modern vehicles, the relay is integrated directly into the body control module or the HVAC blower motor resistor block.
A bad blower motor relay will typically cause your HVAC fan to stop working entirely, blow only intermittently, or get stuck running even when the system is turned off.
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.
Bypassing a blower motor resistor involves connecting the blower motor directly to a 12V power source, forcing the fan to run at its maximum speed. This is typically done as a temporary diagnostic step or an emergency fix when the vehicle's heating/cooling fan stops working.
Yes, you can easily test if a relay is bad using a digital multimeter and a small battery. The best way to be thorough is to test the internal coil resistance first, then verify that the switch properly opens and closes.
Blower motor failure is usually caused by restricted airflow, electrical faults, or mechanical wear. These issues force the motor to work harder, draw excess electricity, and overheat.
Most blower motor relays cost around 15$ to $60.
You will need to locate the corresponding breaker in your circuit box and turn it off as well. Find the Reset Button – you will then need to find the furnace reset button, which is typically located inside the blower compartment, positioned on the side of the blower motor.
To determine if your blower motor is bad, first inspect the system's power, clean the blower wheel, and spin the squirrel cage by hand. If it is seized or stuck, the motor needs replacing. If it spins freely, test the motor using a multimeter or a direct power bypass.
Electrical power is supplied to a blower motor from the vehicle's battery or the home's electrical grid. This power flows through a series of control components—such as a climate control switch, relay, and resistor (or control module)—before ultimately reaching the motor and its capacitor to adjust fan speed and direction.