* Low Voltage/Alternator Issues: When the AC compressor kicks in, it puts a significant load on the electrical system. A weak alternator might not be able to keep up, causing the voltage to drop below what the engine's computer (PCM) can tolerate. This can lead to a sudden stall. Test the alternator's output voltage at idle and with the AC on. It should remain above 13.5 volts.
* Battery Issues: A weak or failing battery can also exacerbate the problem. The added load of the AC compressor might draw the voltage down too far, causing the PCM to shut down the engine to prevent damage. Have the battery tested for its cold-cranking amps (CCA) and its overall health.
* Wiring/Connections: Poor connections in the charging system (alternator to battery, battery to ground) or corrosion in the wiring harness can increase resistance and cause voltage drop under load. Inspect all wiring and connections for corrosion, looseness, or damage. Pay close attention to the main ground cables.
* PCM (Powertrain Control Module): Though less likely, a failing PCM could be misinterpreting the low voltage situation and shutting down the engine as a safety precaution. This is usually a last resort diagnosis, as PCM problems are harder to pinpoint.
* AC Compressor Clutch Issues: While less directly related to stalling, a problem with the AC compressor clutch itself (dragging, excessive current draw) could be causing the initial voltage drop that triggers the PCM to shut down the engine.
Troubleshooting Steps:
1. Test the Battery and Alternator: This is the most crucial first step. Have a qualified mechanic or auto parts store test both.
2. Inspect Wiring and Connections: Carefully examine all battery cables, ground connections, and wiring harnesses related to the alternator and AC system. Look for corrosion, loose connections, or damaged insulation. Clean or repair as needed.
3. Check AC Compressor Current Draw (Advanced): This requires specialized tools, but measuring the current draw of the AC compressor when it's engaged can help determine if it's drawing excessively high current, placing undue strain on the electrical system.
4. Consider a Professional Diagnosis: If you're not comfortable with electrical diagnostics, take your Blazer to a reputable mechanic. They have the tools and expertise to properly diagnose the issue.
Important Note: Driving with a potentially failing alternator or battery is risky. You could become stranded and potentially damage your engine or other components. Address this issue promptly.
