That said, here's a general outline of how to approach checking the expansion valve, keeping in mind this is simplified and doesn't cover all potential scenarios:
1. Preliminary Checks:
* Refrigerant Level: Before touching the expansion valve, you MUST check the refrigerant level in the system. Low refrigerant is the most common cause of poor cooling. This requires AC gauges and a knowledge of how to connect them safely. A low charge is NOT an indication that the expansion valve is bad.
* Compressor Operation: Make sure the compressor is engaging. You can listen for the compressor clutch engaging, or use a mechanic's stethoscope to listen for the compressor's operation. A non-functioning compressor will also prevent cooling.
* Blower Motor: Check that the rear blower motor is working and blowing air. A faulty blower motor will mean cold air can't reach the vents even if the AC system is working correctly.
* Rear AC Controls: Verify the rear AC system is turned on and set to the coldest setting. Check fuses related to the rear AC.
2. Checking the Expansion Valve (Advanced and Potentially Dangerous):
* Visual Inspection: Once the system is depressurized and safely evacuated (by a professional!), you can visually inspect the expansion valve for any obvious damage, leaks, or obstructions. However, this is usually not enough to determine if it's faulty.
* Temperature Difference: After running the system for a while (after professional recharge and leak checking), measuring the temperature of the liquid line and suction line at the expansion valve can offer clues. There should be a significant temperature difference. A minimal difference suggests a problem, which could be the expansion valve. *This requires specialized tools and AC knowledge*.
* Restriction Test (Advanced): A professional AC technician can perform a restriction test using specialized tools to determine if the expansion valve is causing a restriction to refrigerant flow. This is rarely done for DIYers.
* Replacement: If the expansion valve is suspected to be faulty, replacement is usually the solution. However, replacing the expansion valve requires proper evacuation, purging, and charging of the system with refrigerant. This is a job best left to professionals.
Why you should NOT attempt this yourself unless you are experienced:
* Refrigerant Handling: Automotive refrigerants are dangerous if mishandled. They can cause injury, and improper handling can damage the ozone layer.
* System Pressure: The AC system operates under high pressure, and attempting to work on it without proper safety precautions can lead to serious injury.
* Vacuuming and Charging: Properly evacuating the system and charging it with the correct amount of refrigerant is crucial. Incorrect procedures can damage the compressor or other components.
In short: If your 1993 Suburban's rear AC isn't cold, start with the simple checks listed above. If those don't reveal the problem, take it to a qualified automotive AC technician. Diagnosing and repairing an AC expansion valve is best left to trained professionals due to the specialized equipment and knowledge needed, and the potential safety hazards involved.
