Here's a breakdown of why and what to check:
* Blower Motor Resistor: This is the most likely culprit. The resistor pack has multiple resistances that allow for different speeds. If it fails, only the high-speed setting (which usually doesn't go through the resistor) works.
* Wiring Issues: A broken or loose wire in the circuit leading to the resistor or the blower motor itself could also cause this. Check the wiring harness for damage, corrosion, or loose connections.
* Blower Motor: While less likely than the resistor, a failing blower motor could exhibit this symptom. A partially seized motor might only be able to spin fast enough at the highest voltage.
* Fuse/Circuit Breaker: Although less common for this specific issue, a blown fuse or tripped circuit breaker related to the blower motor could interrupt lower speeds.
How to troubleshoot:
1. Locate the Blower Motor Resistor: This is usually found behind the glove box, under the dash, or sometimes near the blower motor itself (consult your repair manual for the precise location on your specific Suburban).
2. Visual Inspection: Inspect the resistor for any signs of burning, melting, or damage. If it looks burnt or smells burnt, it needs replacement.
3. Wiring Inspection: Carefully examine the wiring harness connected to the resistor and the blower motor for any damage, corrosion, or loose connections. Repair or replace any damaged wires.
4. Check the Fuse/Circuit Breaker: Check the relevant fuse(s) or circuit breaker(s) in your fuse box to make sure they're not blown or tripped.
In short: Start by checking the blower motor resistor. It's the easiest and most likely cause. If the resistor is fine, then move on to investigating the wiring and finally the blower motor itself. A repair manual specific to your 1996 Chevy Suburban will be very helpful in locating components and understanding the wiring diagram.
