1. Low Refrigerant Pressure (Despite seeming full): Just because the system *seems* full doesn't mean it is. The gauges on a charging kit are essential. Low refrigerant pressure, even if close to what you think it should be, can prevent the system from working properly. Several things can cause this:
* Leak: This is the most common cause of low pressure. Even a tiny leak can slowly deplete the refrigerant, and the system might not have enough for efficient cooling, even if it seems mostly full. A leak detection dye test is recommended.
* Restricted Flow: A clogged expansion valve, orfice tube, condenser, or evaporator could restrict refrigerant flow, leading to insufficient pressure at the evaporator even if the system is charged.
2. Electrical Issues:
* Low Voltage/Weak Signal: Even with the compressor engaging, the clutch might not be getting enough power to fully engage and provide adequate cooling. Check the voltage at the compressor clutch when the A/C is on.
* Cycling Switch: The pressure switch (or cycling switch) could be faulty and preventing the compressor from running consistently or at all, even with adequate refrigerant. It's designed to shut the compressor off if the pressure gets too high or too low.
* Compressor Clutch Relay: The relay that controls the compressor clutch could be bad. Try replacing it (it's cheap and easy to test).
* Blown Fuse (Again): You said you checked the fuses, but some A/C systems use more than one fuse or even a circuit breaker. Check your car's owner's manual for the complete A/C fuse/circuit breaker diagram.
* Wiring Harness: Check the wiring harness for any breaks, corrosion, or poor connections, especially near the compressor and the A/C controls.
3. Mechanical Issues:
* Compressor Failure: Although it's engaging, the compressor might be internally damaged and not actually pumping refrigerant efficiently. This is less likely if it's engaging, but possible.
* Fan: Does the condenser fan run when the A/C is on? A non-functioning fan will severely reduce cooling efficiency.
4. Blower Motor Issues:
* Blower Motor: While the compressor engaging means the refrigerant part is *partially* working, is the blower motor actually blowing air? It could be a separate problem. Check the blower motor's fuse, relay, and the motor itself. Try adjusting the blower speed.
Troubleshooting Steps:
1. Pressure Test: This is the *most important* step. Use A/C gauges to measure the high and low side pressures. These pressures will tell you if the system is properly charged and working. Without this information, further diagnosis is guesswork.
2. Visual Inspection: Look for leaks around the A/C components. Use a UV dye to help you find them.
3. Electrical Checks: Test the voltage at the compressor clutch and other A/C related components. Check relays and fuses carefully.
4. Fan Test: Check if the condenser fan is working.
5. Blower Motor Check: Verify blower motor functionality.
Warning: Working with refrigerant requires proper equipment and safety precautions. If you are not comfortable working with A/C systems, take your car to a qualified mechanic specializing in automotive A/C repair. Improper handling of refrigerant can be dangerous.
