A Comprehensive Guide to Blower Motor Resistor Wiring Diagrams

Blower Motor Resistor Wiring Diagrams Made Easy

The blower motor resistor controls the speed of the blower motor, which controls how much air is pushed through the HVAC system and into the cabin. Understanding a blower motor resistor wiring diagram is essential for diagnosing issues related to the blower motor’s performance. In this article, we will explore the function of the blower motor resistor, explain the typical wiring diagrams, and offer tips on troubleshooting common problems associated with this component.

The Function of the Blower Motor Resistor

Before diving into wiring diagrams, it’s important to understand the role of the blower motor resistor in a vehicle’s HVAC system:

• Speed Control— The blower motor resistor adjusts the speed of the blower motor by varying the electrical resistance in the circuit. Different resistance levels correspond to different blower speeds. Most vehicles have several speed settings, such as low, medium, and high, and each of these settings is managed by the blower motor resistor.

• Electrical Flow Regulation— The resistor controls the amount of current flowing to the blower motor. By limiting the current, the resistor reduces the speed of the motor. Conversely, when the resistor offers less resistance, more current flows through, resulting in a higher motor speed.

Blower Motor Resistor Operation Simplified

The easiest way to understand what a blower motor resistor does is to think of it as a pipe. For example, think of the blower motor fan wheel as if it’s being driven by a stream of water. One way to reduce the speed of the water jet would be to reduce the size of the pipe supplying the water. That would slow the fan wheel. If you then added an even smaller pipe to the end of the first pipe, it would reduce the flow more. That’s a simplified version of what a blower motor resistor does. It’s a series of small “electrical pipes” that reduce the flow of electricity to the motor.

Typical Blower Motor Resistor Wiring Configurations

While the exact wiring configuration may vary depending on the vehicle make and model, there are some common configurations:

• Series Resistor Setup— In a series resistor setup, the blower motor resistor is connected in series with the blower motor. The resistor has multiple resistive elements, each corresponding to a different blower speed. The HVAC control switch selects which resistor is in the circuit, thereby determining the blower speed.

1) Power from the battery passes through a fuse and then to the blower motor.
2) The blower motor is connected to the blower motor resistor.
3) The HVAC control switch selects the appropriate resistor in the resistor pack.
4) The selected resistor limits the current, thereby controlling the blower motor speed.
5) The circuit is completed by grounding the blower motor.

A blower motor resistor works by routing power through 1, 2, or 3 in-series resistors. See the blower motor resistor wiring diagrams below to see how it works on each speed.

Troubleshooting Blower Motor Resistor Issues

When the blower motor in a vehicle stops working correctly or only works at certain speeds, the blower motor resistor is often the culprit. Here are some common issues and troubleshooting tips:

Blower Motor Only Works on High Speed

Possible Cause: If the blower motor works only on the highest speed, it could indicate that the blower motor resistor has failed. On high speed, the resistor is usually bypassed, so if the resistor is faulty, the motor may only work on this setting.

Solution: Test the blower motor resistor with a multimeter to check for continuity. If the resistor is open or shows no continuity, it will need to be replaced.

Blower Motor Doesn’t Work at All

Possible Cause: If the blower motor doesn’t work at any speed, there could be an issue with the power supply, ground, or the blower motor itself. It’s also possible that the resistor has failed completely, though this would typically affect only some speeds.

Solution: Check the fuse, relays, and power connections first. If these are in good condition, test the blower motor directly by applying power to it. If the motor runs, the issue is likely with the resistor or the HVAC control panel.

Blower Motor Works Intermittently

Possible Cause: Intermittent operation can indicate a loose connection, a failing resistor, or an issue with the HVAC control switch.
Solution: Inspect all wiring connections for looseness or corrosion. Test the resistor and switch for proper operation. If the resistor is corroded or damaged, replace it.

Blower Motor Works at All Speeds Except One

Possible Cause: If the blower motor fails to operate at a specific speed, the corresponding resistor in the resistor pack may be burned out.
Solution: Test each resistor in the pack with a multimeter. If one of them is faulty, replace the entire resistor pack.