1. Rear AC Blower Motor:
* Check: Does the rear blower fan actually turn on? If not, the problem might be a blown fuse, a faulty blower motor, or a bad blower motor resistor. You'll need to check the fuse box (likely under the hood and/or inside the vehicle) for a blown fuse related to the rear blower. If the fuse is good, the motor itself or the resistor may need replacing.
* Testing: You might need a multimeter to check the blower motor and its circuit for power.
2. Rear AC Blend Door Actuator:
* Check: This is a small motor that controls the direction of the air (floor, vents, defrost). A faulty actuator might be stuck in a position that prevents cold air from reaching the rear. You may hear unusual noises from the rear vents.
* Testing: This usually requires visual inspection or potentially replacing it as a whole (a common failure point).
3. Rear Evaporator:
* Check: This is the component in the rear that cools the air. If it's frozen, clogged, or leaking refrigerant, it won't work.
* Testing: This is difficult to check without specialized tools. A low refrigerant level would indicate this as a possible issue.
4. Rear AC Control Panel or Wiring:
* Check: A problem with the rear AC controls themselves (buttons, switches) or the wiring to the rear unit could prevent it from activating.
* Testing: Requires checking the wiring for continuity and damage.
5. Refrigerant Leak Specific to Rear Lines:
* Check: While the front AC works, there might be a leak in the lines *specifically serving the rear* AC unit. This is less likely if the front AC is functioning perfectly but should be considered.
* Testing: Requires a professional AC technician with specialized equipment to check for refrigerant leaks.
Troubleshooting Steps:
1. Check the rear blower fan: Does it turn on? If not, check fuses first.
2. Check the rear AC controls: Are they set correctly? Is power getting to the controls?
3. Listen for unusual noises: Clicking, grinding, or whirrings from the rear may indicate a problem with the blend door actuator.
4. Visual inspection: Access to the rear AC components may require removing some interior panels. Look for obvious problems such as disconnected wires or obstructions.
When to call a professional:
If you're not comfortable with electrical work or AC system diagnostics, it's best to take your Tahoe to a qualified mechanic or AC specialist. Refrigerant leaks, in particular, require specialized tools and handling to avoid environmental damage and personal injury. Replacing components may also require specialized tools and knowledge.
