1. Understand the Symptoms:
* No blower motor function at all (no fan speed): This points strongly towards either a completely failed blower motor or a blown fuse/circuit breaker.
* Blower motor works on some speeds but not others: This is the classic symptom of a failing blower motor resistor. The resistor controls the voltage to the motor, and a bad resistor often results in some speeds working while others don't. Often the highest speed still works, as it bypasses the resistor.
* Blower motor makes a loud noise (whining, grinding): This is more indicative of a failing blower motor. A bad bearing is a common culprit. However, sometimes a heavily stressed resistor can cause unusual sounds.
2. Check the Simple Stuff First:
* Fuse/Circuit Breaker: Locate the blower motor fuse in the fuse box (usually under the hood or dashboard). Check if it's blown. Replace if necessary. Also check for a blower motor relay if your Altima has one (consult your owner's manual).
* Power to the Blower Motor: With the ignition ON, check for power at the blower motor connector using a multimeter. If no power is present, the problem is likely before the motor (wiring, fuse, relay, switch).
3. Testing the Blower Motor Resistor:
This is usually more difficult and often involves removing components to access it. Consult a repair manual specific to your 1994 Nissan Altima for the location and method. A repair manual will typically show you a wiring diagram which is essential for testing. Generally, the resistor is located behind the glove box or under the dash.
* Visual Inspection: Once you have access to the resistor, carefully inspect it for any obvious signs of damage, such as burning, melting, or broken components.
* Ohmmeter Test (Advanced): Using a multimeter, you can test the resistance of each resistor within the resistor pack according to the values specified in a repair manual or wiring diagram. A significant deviation from the specified values indicates a faulty component. Be cautious when working with electrical components and disconnect the battery's negative terminal before proceeding.
4. Testing the Blower Motor:
Access to the blower motor requires more disassembly. Again, a repair manual is crucial.
* Visual Inspection: Look for any obvious damage, debris, or signs of binding.
* Direct Power Test (Advanced and risky): *This should be done with extreme caution.* Disconnect the blower motor connector and, using jumper wires and a battery, carefully apply power directly to the motor terminals (observe correct polarity). If the motor runs smoothly, the motor is likely good. If it doesn't, the motor is faulty. Only do this if you're confident working with electricity.
In Summary:
If only some fan speeds work, the resistor is the most likely culprit. If no fan speeds work, check the fuse/relay first, then the blower motor. A loud noise usually suggests a worn-out blower motor.
Highly Recommended: Consult a repair manual specific to your 1994 Nissan Altima. These manuals provide detailed diagrams, component locations, and testing procedures. This will save you time, frustration, and potentially damage to your vehicle. Online resources like Haynes or Chilton manuals can be helpful.
Remember safety first! Disconnect the negative battery terminal before working with any electrical components. If you're not comfortable performing these tests, take your Altima to a qualified mechanic.
