* Wiring and Connections: This is the most common cause. Even with a new motor, faulty wiring, corroded connectors, or a broken switch can prevent power from reaching the motor consistently. Check:
* The blower motor resistor: This component controls the fan speeds. A failing resistor often leads to intermittent operation or only the highest speed working. It's a common failure point on these cars.
* Wiring harness: Look for frayed wires, broken insulation, or poor connections within the harness leading to the blower motor.
* Blower motor switch: A failing switch may send intermittent signals to the motor.
* Fuse and relay: Although less likely if it sometimes works, a weak fuse or relay can cause this issue.
* Ground Connection: A poor ground connection can prevent the motor from receiving sufficient power. Ensure the ground wire connected to the blower motor and its housing is clean, tight, and free of corrosion.
* Control Module (HVAC Control Module): This is the "brain" of the climate control system. A faulty module can send incorrect signals or no signals at all to the blower motor, even with a new motor and good wiring. This is more of a sophisticated diagnostic issue.
* Incorrect Installation: If the new blower motor wasn't installed correctly, it might not be making proper contact or could be damaged during installation.
* Debris in the Blower Motor Housing: While less likely to cause complete failure, debris can sometimes interfere with the motor's operation.
Troubleshooting Steps:
1. Check the fuses and relays: Start with the simplest checks.
2. Inspect the wiring harness and connectors: Look for visible damage, corrosion, or loose connections. Pay close attention to the connections at the blower motor resistor.
3. Test the blower motor resistor: This is often a simple resistance check with a multimeter. Replace if faulty.
4. Clean the ground connection: Make sure the ground connection is clean and tight.
5. Check the blower motor switch: This may require some electrical testing or replacement to rule out.
6. Inspect the blower motor housing: Check for obstructions.
If you're not comfortable with electrical work, it's best to take the vehicle to a qualified mechanic. They have the tools and experience to diagnose the problem properly and prevent further damage. Simply replacing the blower motor without addressing underlying electrical problems is a common waste of time and money.
