* Alternator: Even though your truck starts right back up, a failing alternator might not be charging the battery sufficiently. The added load of the AC compressor puts extra strain on the system. A failing alternator can cause erratic voltage, leading to the stalling. Get the alternator tested for proper output (voltage and amperage).
* Battery: While you replaced the battery, it's possible the new battery is faulty or not properly sized for your vehicle. A weak battery, even a new one, can struggle under the load of the AC. Have the battery's charging system tested to make sure it's accepting a charge correctly.
* Dirty or corroded battery terminals/connections: Even with a new battery, poor connections can restrict current flow, causing similar problems, especially under load. Clean and tighten all battery terminals and connections. Use a wire brush and battery terminal cleaner.
* Idle Air Control (IAC) Valve: This valve regulates the engine's idle speed. A malfunctioning IAC valve could cause the RPMs to drop too low when the AC compressor kicks in, leading to stalling. Cleaning it (if possible) or replacement might resolve the issue.
* Throttle Position Sensor (TPS): An inaccurate reading from the TPS can affect the engine's fuel mixture and idle speed. A faulty TPS could cause erratic idle and stalling, particularly under load.
* Mass Airflow Sensor (MAF) Sensor: A dirty or faulty MAF sensor can provide incorrect readings to the engine control unit (ECU), leading to poor fuel delivery and stalling. Cleaning the sensor (carefully, following instructions) can sometimes fix this.
* Low Fuel Pressure: While less likely, it's possible there's a fuel pressure issue that becomes apparent under load (AC on).
Troubleshooting Steps:
1. Check Battery Terminals/Connections: Clean and tighten them thoroughly. This is the easiest and cheapest thing to check first.
2. Have the Alternator Tested: This is crucial. A failing alternator is a common cause of these symptoms.
3. Have the Battery Tested: Even a new battery can be defective. Make sure it's holding a proper charge and the charging system is working correctly.
4. Inspect the IAC Valve: See if it's dirty or easily accessible for cleaning. Replacement might be necessary.
5. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to check for any stored trouble codes. This can provide valuable clues.
If you're not comfortable performing these checks yourself, take your Trailblazer to a qualified mechanic. The problem is likely related to the charging system or a sensor issue. Don't ignore it, as continued stalling could damage your engine.
