* Low Coolant: This is the most basic and important check. Low coolant means less capacity to absorb heat, leading to overheating, especially under stress like AC use. Check your coolant level (when the engine is cold!) and add coolant if needed. *Do not* just add water; use the correct 50/50 mix of coolant and distilled water. A leak somewhere in the system (radiator, hoses, water pump, etc.) is the likely cause of low coolant.
* Failing Water Pump: The water pump circulates coolant through the engine. A failing pump may not circulate coolant effectively, leading to overheating, especially when the engine is working harder (like with the AC on). Look for leaks around the pump, or listen for unusual noises (whining or grinding).
* Clogged Radiator: A radiator clogged with debris reduces its ability to dissipate heat. This is more likely if you haven't flushed your radiator in a while. A pressure test can determine if the radiator is the issue.
* Faulty Radiator Fan: The radiator fan helps cool the radiator. If it's not working, or not coming on when it should (often controlled by a temperature switch or the AC system), the radiator won't cool effectively, especially at idle or low speeds where airflow is minimal. Check if it's running when the engine is hot, and that the fan clutch is functioning.
* Thermostat Issues: A stuck closed thermostat prevents coolant from circulating until it reaches a very high temperature. This can lead to overheating, particularly when the engine is under additional load from the AC.
* AC Compressor Issues: While less likely to be the *direct* cause of overheating, a very inefficient or failing AC compressor can put excessive strain on the engine, contributing to overheating. This is less common than the cooling system problems listed above.
* Head Gasket Failure: A blown head gasket can allow coolant to leak into the engine or vice versa. This is a serious issue and would usually be accompanied by other symptoms like white smoke from the exhaust, milky oil, or loss of coolant without visible leaks.
Troubleshooting Steps:
1. Check coolant level: The most important first step.
2. Inspect hoses and connections: Look for cracks, leaks, or loose clamps.
3. Check the radiator fan: Does it turn on when the engine is hot?
4. Check the thermostat: Make sure it opens at the correct temperature.
5. Listen for unusual noises: Whining from the water pump is a bad sign.
6. Look for external leaks: Inspect the entire cooling system carefully.
If you're not comfortable working on your car yourself, take it to a mechanic. Overheating can cause serious engine damage. Diagnosing the exact problem might require pressure testing the cooling system and other more advanced diagnostics.
