1. Check the Obvious:
* Rear Blower Fan: Is the rear blower fan actually running? If not, the problem might be a blown fuse, a faulty fan motor, or a problem with the fan switch.
* Temperature Settings: Make sure the rear AC controls are properly set to "cold" and that the rear blower is turned on.
* Rear AC Switch: If your Tahoe has a separate switch to engage the rear AC, make sure it's turned on.
2. System-Specific Issues:
* Low Refrigerant: The most common cause of a non-functioning AC system is low refrigerant. This requires a professional recharge and leak check. A leak anywhere in the system (lines, compressor, evaporator) can cause this.
* Compressor Clutch: The compressor clutch engages to allow the compressor to run. If it's not engaging, the compressor isn't circulating refrigerant. This could be due to a faulty clutch, low refrigerant, or a problem with the compressor itself.
* Blend Door Actuator: This component controls the airflow direction. If it's malfunctioning, it might be preventing cold air from reaching the rear vents, even if the system is otherwise working.
* Evaporator: The evaporator is the component that cools the air in the rear. A clogged or failing evaporator will prevent cold air from reaching the rear vents.
* Wiring/Electrical Problems: Faulty wiring, connectors, or fuses related to the rear AC system could interrupt power to various components. This could also include the rear AC switch itself.
3. More Advanced Troubleshooting:
* Pressure Tests: A professional AC technician can perform pressure tests to determine if the system is low on refrigerant or has a leak.
* Electrical Diagnostics: Using a multimeter, a professional can check for power at various points in the rear AC circuit. This can help pinpoint faulty wiring, fuses, or switches.
Where to Start:
1. Check the fuses: Locate the fuse box(es) in your Tahoe and check the fuses related to the rear AC system (consult your owner's manual). Replace any blown fuses.
2. Listen for the compressor: When the front AC is running, you should hear a clicking sound (the compressor engaging). If you don't hear this sound when the rear AC is turned on, there's likely a problem with the compressor clutch or system pressure.
3. Check the rear blower: If the blower isn't working, focus on that problem first.
Recommendation:
Unless you have significant automotive experience, it's best to take your Tahoe to a qualified automotive AC technician. Diagnosing and fixing AC problems can be complex and require specialized tools and knowledge. Attempting repairs yourself could lead to further damage or injury.
