Honda Blower Motor Diagnostics and Replacement

Step-by-Step Guide to Troubleshooting and Fixing Your Honda Blower Motor

The Honda Blower Motor design in post-2000 model years is different than previous generations that used a simple speed switch and a blower motor resistor. In this article, I’ll explain how the newer systems work and how to diagnose the root cause when your Honda blower motor doesn’t work.

Understanding the Honda Blower Motor Components

• Blower Motor— The blower motor itself is a robust electric motor that powers the fan. It’s driven by DC voltage from the vehicle’s electrical system. When the motor spins, it pushes air through the HVAC ducts.
• Blower Motor Resistor Power Transistor— This is where the magic of speed control happens. Older Hondas use resistors, while newer models rely on advanced power transistors. These components control the amount of voltage the blower motor receives, which in turn determines its speed.
• HVAC Control Panel— This is your interface. Whether you’re turning a dial, sliding a lever, or tapping a touchscreen, the control panel sends your input to the system, selecting the desired blower motor speed.
•  Blower Motor Relay— High-speed blower operation demands a lot of current. The relay handles this high current without frying the rest of the system. Think of it as the circuit’s muscle.
• Fuse— A fuse is a must-have safety feature, protecting the circuit from electrical overloads or short circuits. In the Honda blower motor system, you’ll usually find a fuse for the blower motor control coil, a separate fuse for the blower motor relay contacts, and at least one fuse for the HVAC Control Panel.

How the Honda Blower Motor System Works

I will now break down the Honda blower motor circuit for you. It all starts with the HVAC (heating, ventilation, and air conditioning) control head, also called the Climate Control Head. This is where you set your desired temperature and blower fan speed.

When you turn on the system and select a blower fan speed, the control head provides a ground path to the blower motor relay control coil. With power and ground to the relay control coil, the relay contacts close, providing power to the blower motor. The blower motor can now operate, but its speed is determined by how long the power transistor closes the ground circuit. Here’s how it does that.

The Honda Climate Control Head varies blower motor speed with pulse width modulation

In simple terms, if the driver selects the middle fan speed, the HVAC control head commands the power transistor to turn the ground connection on and off: .5/second on and on .5/second off. So the blower motor spins at half speed. If the driver selects a slower speed, the HVAC control head commands the power transistor to turn the ground connection on and off at a different rate, like  .75/second off and .25/second on.

Testing the Honda Blower Motor System

If the blower motor doesn’t work

Start by checking for a blown fuse to the blower motor relay (1). If the fuse is good, unplug the electrical connector at the blower motor and check for power coming from the blower motor relay (2) with the IGN in the RUN position and the blower motor turned on to any speed. If you see battery voltage, move on to check for good ground at the power transistor (3).  It you don’t see ground, replace the blower motor power transistor.

If that doesn’t fix the problem, then the Climate Control Head or the wiring harness between the head and the transistor is the problem. Unfortunately, the only way to test for a properly operating control head is with a scope, which is best left to a shop.

If your Honda blower won’t shut off

This is rare, but it can indicate a short-to-ground inside the power transistor. Replace the power transistor.

How Older Honda Blower Motors Work

Older Hondas used a traditional speed switch, fuse, blower motor relay, blower motor, and blower motor resistor.

How a blower motor resistor system works

Most carmakers install the blower motor resistor in series with the ground side of the circuit. Depending on the fan speed you choose, the ground circuit can flow through 4 resistors for low speed and no resistors for high speed. See how the current flows in the blower motor wiring diagrams below.

OFF: The blower motor doesn’t have power because the blower motor relay has not been turned on.

Low Speed 1: Power flows to the blower motor and then passes through all four resistors, then to the switch, and finally to the ground. The four resistors cause the motor to run at it’s lowest speed.

Speed 2: Power flows to the blower motor and then passes through two resistors, then to the switch, and finally to the ground. The two resistors cause the motor to run at middle speed.

Speed 3: Power flows to the blower motor and then passes through one resistor, then to the switch, and finally to the ground. The single resistor causes the motor to run at a faster speed.

High Speed: Power flows to the blower motor and bypasses all the resistors, then to the switch, and finally to the ground. This causes the motor to run at its highest speed.

This setup is effective but not without its downsides. Resistors generate heat, and energy efficiency isn’t their strong suit.

Replacing a Honda Power Transistor or Blower Motor Resistor

Whether your Honda has a resistor or power transistor, replacement is as simple as removing the glove box door and trim panels to access the resistor or transistor. The resistor and transistor are usually located near the blower motor under the dash on the passenger side of the cabin. Both the resistor and transistor mount to the ductwork so they can be cooled by the airflow.

To replace
• Disconnect the electrical connector to the resistor or transistor.
• Remove the two screws securing the resistor or transistor in place.
• Clean out any leaves or debris in the air duct.
• Swap in the new resistor or transistor
• Connect the electrical connector
• Test by running the blower motor at various speeds

The Take Aways From This Article

The Honda blower motor on post 2000 model year vehicles operates using a power transistor instead of a blower motor transistor. circuit is a testament to thoughtful engineering. From the resistor-based systems of older models to the advanced PWM-driven designs of today, it’s clear that Honda prioritizes efficiency, reliability, and user comfort. Understanding how this system works isn’t just interesting—it’s practical knowledge that can help you troubleshoot and maintain your vehicle’s HVAC system.

Whether you’re chasing down an issue or simply curious, mastering the ins and outs of the blower motor circuit puts you in the driver’s seat, ensuring your Honda’s climate control system runs smoothly for years to come.

©, 2024 Rick Muscoplat