1. Power Supply & Circuitry:
* Fuse: Check the blower motor fuse in the fuse box (underhood and/or inside the vehicle). A blown fuse is the easiest and cheapest fix.
* Relay: Locate the blower motor relay (often in the underhood fuse box). A bad relay can also prevent the blower from working. You may need to test the relay with a multimeter or swap it with a known good one of the same amperage.
* Wiring: Visually inspect all wiring connected to the blower motor resistor, the blower motor itself, and the switch. Look for any signs of damage, such as fraying, melting, or corrosion. Pay close attention to the connections – ensure they are clean and tight. Test the continuity of the wires using a multimeter.
* Blower Motor Resistor: This component controls the fan speeds. A faulty resistor can cause the blower to work on only one speed (often high) or not at all. These are relatively inexpensive to replace and are often located near the blower motor.
2. Blower Motor itself (Before Removal):
* Check for obstructions: Make sure nothing is blocking the blower wheel (leaves, debris, etc.). Sometimes a small obstruction can prevent the motor from turning even if it's working. You may be able to feel for obstructions by gently rotating the blower wheel with your fingers. (Be careful not to force anything.)
* Listen for unusual sounds: Before pulling it out, try turning the ignition on. Is there any clicking, grinding, or whining? These could indicate a bad bearing or other internal motor failure.
3. Blower Motor Switch:
* Switch Operation: Test the blower motor switch on all speeds. If it only works on the highest setting, the resistor is likely the problem. If none of the settings work, the problem could be with the switch itself, the wiring to the switch, or something further upstream.
4. Other Considerations:
* Ground Connection: A poor ground connection can prevent the blower motor from working. Inspect the ground wire connected to the blower motor and ensure it's clean and secure.
* HVAC System: Ensure the HVAC system is set to blow air (not recirculate).
Important Note: If you're not comfortable working on electrical systems, it's best to take your Blazer to a qualified mechanic. Incorrectly diagnosing or repairing electrical components can lead to further damage or even injury. Remember safety first! Always disconnect the battery's negative terminal before working on the electrical system.
