These are different components. The blower motor high relay will affect high speed blower operation. The blower motor resistor will vary the lower speeds.
The blower motor relay is the electrical switch that is used to supply the power for the vehicle's blower motor. The blower motor is the component responsible for pushing air through the vents of your vehicle's heating and air conditioning systems.
When the blower doesn't work, check to see if it's getting power. If it's getting power, but not blowing, then the motor is probably bad. If it's not getting power, then the relay is probably bad.
Blower Motor Resistor Test
Typically, if the fan will work on some speeds but not on others, the resistor is suspect. Okay, let's say there's no melting going on, but your fan doesn't work on all speeds. Typically, if the fan will work on some speeds but not on others, the resistor is suspect.
The blower motor can indeed function without the resistor. As we know, the resistor is responsible for controlling the blower motor's speed by regulating the voltage supplied to it. It will turn out that without the resistor, the blower motor may run at maximum speed or not function as expected.
Should I drive if my blower motor resistor is broken? You can drive, of course, but you might not be able to regulate the fan speeds in your car, which could interfere with both comfort and defrosting power.
These are different components. The blower motor high relay will affect high speed blower operation. The blower motor resistor will vary the lower speeds.
Checking a Resistor
Turn off power to the resistor and disconnect it from the circuit. Then, connect the 2 leads on a multimeter to the 2 legs on the resistor. Also, look for signs of damage on the resistor, like blackening or charring.
These include: The blower motor itself: Check if it is faulty or damaged. The wiring connections: Ensure that all the wiring connections are secure and free from corrosion. The fuse: Inspect the fuse related to the blower motor resistor and replace if necessary.
You can also test your relay's functionality by switching your multimeter to test for resistance. This process involves switching your multimeter to read ohms and connecting the two leads to pins 85 and 86. A functioning relay coil should have a reading of between 50 and 120 ohms, but usually it's very near 75 ohms.
Strange Rattling, Clanking, or Screeching
One of the first signs you may notice when there's an issue with the blower motor is a strange noise coming from the indoor unit or air handler.
If the cooling fan relay has failed, you may see warnings, such as the check engine light and the temperature warning light, pop up on the dash, but first, you may notice that the A/C stops cooling. More about that in the next paragraph. The check engine light illuminating may indicate a faulty cooling fan relay.
On some platforms, a faulty blower motor relay will cause the blower not to work at all, which means there will be no airflow from the A/C. On others, the blower won't work on “high blow” but all the other speeds will work. The blower motor relay fails because it regularly deals with high current loads.
Blower motor resistors have several resistors with different resistances. 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.
Causes of blower motor resistance failure
Corrosion and Moisture: Vehicle interiors may experience moisture and humidity, which may cause corrosion on the blower motor resistor contacts or circuit boards. Corrosion can destroy electrical connections and prevent the resistor from functioning properly.
The main symptoms of a bad blower motor resistor include:
Only One Speed From Blower Motor. Various Airflow Settings Not Working. No Air Coming From Vents.
This can have several consequences. The resistance value can shift permanently, the lifetime can be significantly reduced, or the resistor is completely damaged resulting in an open circuit. In extreme cases the excessive power can even melt or catch on fire.
In HVAC systems, a blower motor relay is an electrical component that controls the operation of the blower motor. The blower motor is responsible for circulating air through the HVAC system, whether it's for heating or cooling.
Likely they are burned or corroded, which would cause a poor connection, overheating and burning the relay contacts. Also, check any grounds for the harness. If they are corroded, repair them. Also, blower resistor pack could be defective to the point it is overheating the relay.
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 average cost for a Blower Motor Resistor Replacement is between $119 and $154. Labor costs are estimated between $43 and $54 while parts are priced between $76 and $99. This range does not include taxes and fees, and does not factor in your unique location. Related repairs may also be needed.
What Causes Failure in Heater Resistors / Regulators. Heater resistors and regulators can fail for different reasons. We'll go over the most common causes of failure, like overheating from blocked airflow, rust due to water damage, broken seals and more.
The heater resistor is also known as the heater blower motor resistor or blower speed controller because it fundamentally controls the fan speed of the interior heater. In this TechASSIST guide we look at the types of resistors, causes and symptoms of failure and offer advice on diagnosing faults.