A failing blower motor control module typically causes erratic HVAC behavior, including the fan getting stuck on one speed, operating only at maximum speed, blowing with weak airflow, or shutting off completely. It can also cause the fan to run continuously even when the car is turned off.
Diagnosing ECM & X13 Motors
This controls the current that runs through the blower motor. Each fan speed selection is connected to one or more of the resistors in the blower resistor assembly. The change in resistance controls the current through the blower motor, which in turn limits the speed that the blower motor spins at.
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.
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.
Knowing the common causes of blower motor failure and how to fix them can save much time and money.
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.
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.
When a vehicle's control module goes bad—such as the Engine Control Module (ECM) or Body Control Module (BCM)—the car's "nervous system" malfunctions. This results in erratic electrical behavior, sudden engine stalling, poor fuel economy, or the vehicle failing to start entirely.
A blower motor resistor or a blower motor control module/regulator is the part that controls the speed of the blower motor. A blower motor resistor is a simple electronic resistor. It is used in cars where the blower motor has only 4 or 5 fixed speeds.
A bad fan control module typically causes engine overheating, non-stop fan operation, or complete fan failure. To determine if yours is failing, look for specific symptoms like erratic fan speeds or poor A/C performance, then perform basic electrical and diagnostic tests.
The least invasive way to diagnose an ECM failure is to connect an onboard diagnostic (OBD or OBD II) tool to the diagnostic port. From there, you can scan to see if your engine computers have produced any error codes.
Common Signs of a Failing HVAC Blower Control Switch
Testing a blower motor resistor involves checking for physical damage and using a multimeter to verify electrical resistance. If your fan only operates on the highest setting or not at all, a faulty resistor is likely the culprit.
When a resistor goes bad, its internal resistance changes. It will generally either fail open (stop the flow of electricity entirely) or drift in value (block too much or too little current). This can cause the circuit to malfunction, overheat, or fail completely.
Resistors most often fail open, not closed as in a short circuit. So if you just wanna take a quick and dirty look, you can place a resistance meter across the component and you should get the resistor's rated value OR LESS.
To quickly tell if your car's HVAC issue is the blower motor or the resistor, look at your fan speed settings. If the fan works only on the highest setting, the resistor is usually the culprit. If the fan fails completely on all speeds, or struggles and stutters, the blower motor is likely failing.
Disconnect the blower motor from its power source. Attach the multimeter probes to the motor terminals. A reading close to zero indicates good continuity, meaning the motor windings are intact. A reading of infinity suggests a break in the winding.
The blower relay plays a vital role in the Heating, Ventilation and Air Conditioning (HVAC) system of modern automobiles. It controls the operation of the blower and ensures a comfortable environment for the driver and passengers.
In this case, we see the resistor value by a multimeter and try to compare it to its actual value. If the measured multimeter value matches the given actual value of the resistor we say the resistor is good, else you have a bad resistor.
A blower motor resistor (also called a blower resistor pack) is a set of high-power resistors—and usually a thermal fuse—mounted in the air stream of your HVAC duct.