Understand Blower Motor Circuits to Better Diagnose Problems (Season 5/E12)

Summary

In this episode of Tech Garage, presented by RockAuto, the focus is on diagnosing issues with automotive air conditioning systems. The host explains the process of troubleshooting electrical components, using a detailed schematic of an air conditioning circuit. By systematically testing voltage and checking components like the blower motor, resistor block, and high-speed relay, the host demonstrates how to identify and fix common issues. The episode also touches on advancements in automotive systems, such as the shift from resistor blocks to pulse width modulation for better efficiency and cooling. The episode emphasizes the importance of methodical diagnostic approaches and practical tools, like RockAuto's service manuals.

Takeaways

• 😀 Strategy-based diagnosis is key to fixing electrical components like blower motors. It involves identifying good parts to find faulty ones.
• 😀 An air conditioning board setup is used to demonstrate how to diagnose problems with components like the blower motor, resistor block, and high-speed relay.
• 😀 When diagnosing a non-working blower motor, check the purple wire for voltage. Zero volts indicate no power to the motor.
• 😀 Checking the ground side is important for verifying the circuit's functionality. A 12-volt reading means the ground side is working.
• 😀 Diagnosing different fan speeds involves testing the voltage at various wires. Lower voltages indicate slower fan speeds.
• 😀 At high speed, the blower motor should receive 12 volts. This is a sign of a functioning high-speed circuit.
• 😀 For slower fan speeds, voltage readings drop at the resistor block (e.g., 5 volts for the first speed).
• 😀 As fan speeds increase, the voltage increases, which makes the motor run faster.
• 😀 Newer cars use pulse width modulation (PWM) instead of resistors to control fan speed, making the system more efficient and cooler.
• 😀 The transition from resistor blocks to PWM systems in newer cars reduces heat and simplifies the blower motor's operation.
• 😀 Schematics are essential for diagnosing issues. A wiring diagram can help you trace components, like in a case with a fuel pump, to pinpoint the real issue.

Q & A

What is the main purpose of the strategy-based diagnostic approach in this video?

The strategy-based diagnostic approach is used to systematically identify faulty components in a vehicle’s blower motor system by checking voltage levels at different points in the circuit. This method helps to pinpoint issues like a faulty blower motor, resistor block, or relay by ruling out good components first.

How does the resistor block affect the blower motor in the air conditioning system?

The resistor block regulates the speed of the blower motor by stepping down the voltage. As the voltage decreases through the resistor block, the blower motor operates at slower speeds. This is why different wires corresponding to different speeds show different voltage readings.

What does the voltage reading on the purple wire indicate in the diagnostic process?

The purple wire connects directly to the blower motor, and checking the voltage on this wire helps determine whether the motor is receiving power. If the voltage is zero, the motor will not operate. A reading of 12V means the motor is receiving power and is working at full speed.

What is the significance of checking the ground side of the system during diagnosis?

Checking the ground side of the system is important because it confirms whether the ground connection is intact. If the ground is good and shows 12V when tested, it indicates that the ground side of the circuit is functioning correctly, which is essential for the proper operation of the blower motor.

What role does the high-speed relay play in the blower motor circuit?

The high-speed relay controls the flow of electricity to the blower motor. When the relay is engaged, it bypasses the resistor block, allowing full 12V power to reach the motor for high-speed operation. If the relay is malfunctioning, the motor may not receive the correct voltage for high speeds.

How does the voltage on the brown, tan, and light blue wires correlate with blower motor speed?

The voltage on the brown, tan, and light blue wires indicates different blower motor speeds. As you move from the brown wire (low speed) to the light blue wire (high speed), the voltage increases from about 5V to 12V. The varying voltage levels correspond to the different speeds of the blower motor.

What is the difference between older resistor-based systems and modern PWM (Pulse Width Modulation) systems for controlling blower motor speed?

Older systems used resistor blocks to step down the voltage and control blower motor speed, generating heat as a byproduct. Modern vehicles use Pulse Width Modulation (PWM) to control the blower motor speed by pulsing the motor on and off at varying intervals, which is more efficient, generates less heat, and is controlled by the vehicle’s computer.

Why is it important to use a wiring schematic when diagnosing vehicle electrical problems?

A wiring schematic is essential because it provides a clear, detailed layout of the electrical components and their connections. It helps diagnose electrical issues by showing the path of electricity, potential points of failure, and how various components interact, making it easier to identify and fix problems.

What was the problem with the fuel pump in the presenter’s real-world example, and how did the schematic help diagnose it?

In the presenter’s example, the fuel pump wasn't working due to corrosion in the connector going into the engine computer. The schematic helped by showing that the wiring diagram for the inertia switch in the trunk was incorrectly labeled, leading the presenter to trace the correct path for diagnosing the issue.

How can car owners and technicians access the necessary schematics and service manuals mentioned in the video?

Car owners and technicians can access the necessary schematics and service manuals through resources like RockAuto, which provides detailed diagrams and service information for a wide range of vehicles, helping to facilitate accurate diagnosis and repair.