Why does my car heater only work on the highest setting?
The blower motor resistor is prone to shorts, corrosion, and overheating. When the resistor fails, typically, the highest setting is the only option that still functions. This is because the air from the blower motor is bypassing the resistor, thus gaining the maximum amount of voltage, resulting in full power.
What causes a blower motor to only work on high?
Most car manufacturers use a series of resistors to make the heater blower motor run at different speeds. And when one or more of these resistors burn out, you’re usually left with only one heater blower motor speed—high. The resistor module is easy and inexpensive to replace.
Does blower motor resistor affect heater?
Blower motor resistor / control module problems In some cars, a failed blower motor resistor can cause a heater fan to stop working completely. In most cases, a blower motor resistor fails due to corrosion or overheating.
How do I know if my heater blower motor is bad?
What Are Signs Your Blower Motor Needs to Be Replaced?
- 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.
How do I know if it’s the blower motor or the resistor?
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.
How do you test a blower motor on a heater?
How to Test a Blower Motor
- Use voltmeter or ohmmeter to check for a blown fuse. If you find one, replace it.
- Start car and see if blower motor works.
- If the circuits are in good repair but the blower motor keeps blowing fuses, replace the blower motor [source: You Fix Cars].