The most common symptom of a bad blower motor resistor is the blower motor will only work at one or two speeds. It can also cause the blower motor to stop working completely and you will notice no air coming from the vents.

How do you tell if the blower motor is bad or the resistor?

If the airflow from the vents is weak… If you try to increase the air pressure and you feel no difference in the pressure blowing, then your blower motor resistor may be failing. A damaged blower motor resistor will work on one fan speed which may not be enough to keep the inside of your car cool or warm enough.

What happens when blower resistor goes bad?

Power to the blower motor is fed through the blower motor resistor, so if it fails or has any issues power can be cut off to the motor. A blower motor without power will not be able to produce any air pressure, and as a result the heating and air conditioning system will be left with no air coming from the vents.

Can a blower motor resistor be bypassed?

Blower resistors are made of several resistors with different resistances. … In the highest speed state, the blower resistor is bypassed completely and the fan is connected directly to the car’s battery, which allows maximum current through the motor.

Why does my blower motor resistor keep burning out?

Trent, one of the biggest reasons for blower motor resistors to have shorten life is actually because of faulty blower motor drawing too many amps, some times melting wires/plugs, heating up resistors shortening their life.

How do you know if a resistor is bad?

Your meter will read it as open circuit (infinite ohms). Or maybe it’s a 0.1 ohm current sensing part. Your meter will read it as a short circuit. If it’s a larger resistor with leads and it looks and smells burnt, assume it’s bad.

What are the symptoms of a bad blower motor?

• Poor or Airflow from Air Vents. This will be the first and most obvious sign your blower motor has a problem. …
• No Airflow At All From Vents. …
• Skyrocketing Energy Bills. …
• Strange Noises When You Turn on the Heat. …
• Overheating Blower / Weird Smells.

Can you bypass a resistor?

All current will bypass the resistor and travel through the short. The voltage across the 100Ω resistor is going to be zero. The 100Ω resistor is not impacting the circuit.

What happens if a resistor burns out?

When a resistor breaks down, current typically flows through the burnt resistor without any resistance and thereby passes unchecked. Other components in the circuit may become damaged from the excess current flowing through.

Why does my car AC blower only work on high?

When a blower resistor fails, the highest fan speed usually is the only one that still works because it essentially bypasses the resistor and receives the maximum amount of voltage. When the resistor is working, it reduces the amount of voltage going to the lower fan speeds, so the fan runs slower.

Article first time published on

Does a blower motor resistor have a fuse?

A fuse is often located on the resistor board. The fuse only protects the low and medium blower speeds. High speed will still work if the resistor fuse is blown.

Why is my blower not working in my car?

If little air is coming through the vents (hot or cold), then it could be because the blower motor for the fan or a switch or resistor that controls fan speed isn’t working. Another cause might be that the electronically controlled “blend doors” that direct air flow are stuck or broken.

How do I reset my blower motor?

1. Step 1: Turn off the power to the furnace. …
2. Step 2: Remove the blower compartment cover. …
3. Step 3: Make sure the blower is completely cooled off. …
4. Step 4: Locate the reset button. …
5. Step 5: Press the button in (assuming that this is your issue and that the button has popped).

How do I test an AC resistor with a multimeter?

Place one lead of the Ohmmeter on terminal 1 of the resistor. Place the other lead on terminal 2 and check against specifications. If this circuit is open, showing infinity on the Ohmmeter, the blower resistor must be replaced. Move the lead from terminal 2 to terminal 3 and check this reading against specifications.

What happens when blower motor relay goes bad?

If you have a faulty blower motor, you may experience low airflow from the vents, even when the fan is on high. There will be no air coming from the vents if your fan isn’t working due to a bad blower motor resistor.

How do you know if a resistor is shorted?

If its two terminals are connected to the same node, the resistor is short-circuited. In practical circuits, we might also say a resistor is short-circuited if a much lower value resistor is connected in parallel with it.

How do you keep a resistor from overheating?

Resistive losses can be reduced by the choice of appropriate voltages. It is much better to feed a low voltage low current device like an LED from a low voltage, through a low value resistor, than from a high voltage through a high value resistor. With an LED the light output is the property of interest.

What causes a resistor to fail?

A fixed composition resistor normally fails in an open configuration when overheated or overly stressed due to shock or vibration. Excessive humidity may cause an increase in resistance. A variable composition resistor may wear after extensive use, and worn away particles may cause high resistance short circuits.

What causes resistors to heat?

On a microscopic level, electrons moving through the conductor collide (or interact) with the particles of which the conductor (metal) is made. When they collide, they transfer kinetic energy. The electrons therefore lose kinetic energy and slow down. … The transferred energy causes the resistor to heat up.

What are the signs of a bad climate control module?

Common signs include inconsistent cooling, out-of-date software, and uneven air distribution, since the module controls the whole AC system.

What happens when a resistor is open?

Resistors fail open circuits, but a high value Resistor, with a voltage across it exceeding its maximum voltage rating, can fail short, which can drastically reduce the resistance value.

Can load resistors go bad?

They shouldn’t go bad, but it could be an issue that as the resistor heats up with prolonged use that some thing shorts out or makes contact. They’re cheap and easy enough to swap out.

Can a resistor cause a short?

Resistors typically do not short. If anything they burn open. You can certainly check them when the circuit is turned off with an ohm meter. With the circuit turned on using a volt meter you can (sometimes) observe a voltage drop across the resistor.

Why does my AC only work when the car is moving?

When the car is moving, versus stopped, there is more air flow over the condenser (the heat exchanger in front of the radiator) and that airflow is essential to system operation. … Other possibilities are that the compressor clutch is not cycling as intended or that the condenser might be blocked or dirty.

Why does my AC only work when I'm driving fast?

You could have a low system freon, When the engine is turning faster, the compressor can build up the pressure enough to have cool air out the vents. Or you might not have condenser fans working correctly not pulling cool ari across the condenser while slow or parked.

What is blower resistor?

The blower motor resistor is responsible for controlling the blower motor speed. … 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.

Where is the blower motor relay fuse located?

The blower relay is located near the front of the fuse block and is labeled “Blower.” Inspect the center of the relay. If the metal rod inside is broken, the relay will need to be replaced.

What relay controls the blower motor?

The blower motor relay controls the current used to power the blower motor, and is subject to the constant on and off switching. Over time, it can eventually wear out.

Where is the blower fuse located?

Many vehicles have two fuses for the blower motor, one in the interior fuse block and the other under the hood. The blower motor is usually under the dashboard on the passenger side.