* Low Refrigerant: This is the most common reason for an AC system to not cool properly. Even a small leak can significantly impact performance. You'll need an AC system pressure test to determine if this is the issue.
* Compressor Failure: The compressor is the heart of the AC system. If it's not working correctly, it won't circulate refrigerant, resulting in hot air. A mechanic can diagnose compressor issues with specialized tools.
* Condenser Problems: The condenser (located in front of the radiator) dissipates heat from the refrigerant. A clogged or damaged condenser can prevent proper cooling.
* Blower Motor Resistor: While less likely to cause *only* hot air, a faulty blower motor resistor could affect the blower's ability to properly circulate cool air. If the fan isn't blowing strongly enough, even if cold air is present, you'll feel warm air.
* Blend Door Actuator: This controls the mix of hot and cold air. A malfunctioning blend door actuator might be stuck on the hot air setting, regardless of the temperature controls.
* Evaporator Coil Issues (Despite Replacement): While you replaced the thermostat, there might be other problems with the evaporator coil itself, such as leaks or restrictions within the coil. It's possible the replacement was faulty or another related component was damaged during installation.
What to do:
1. Check the refrigerant level: This is the first and easiest check. You'll likely need a gauge to do this properly. Adding refrigerant without addressing a leak is only a temporary fix.
2. Have a professional diagnose the problem: An automotive AC specialist can perform a thorough inspection, identify the fault, and perform the necessary repairs. Trying to troubleshoot this further on your own can be complex and potentially lead to more damage. They have the equipment and expertise to identify problems like compressor issues or refrigerant leaks that are difficult to detect otherwise. Don't just add refrigerant; finding the leak is crucial.
Ignoring a faulty AC system can lead to further damage and costly repairs in the long run. Professional diagnosis is highly recommended.
