Here's a breakdown of likely causes and what to do:
* Low Refrigerant: This is the most probable cause. A leak somewhere in the system (hose, seal, condenser, evaporator) has allowed refrigerant to escape over time. A mechanic needs to diagnose and repair the leak before adding refrigerant; otherwise, you'll just keep losing it and wasting money.
* Compressor Clutch Issues: While less likely given your description, a failing compressor clutch might not engage properly at idle, leading to reduced cooling. This would usually manifest as no AC at all, or weak cooling, even when driving.
* Condenser Fan Problems: The condenser fan helps cool the refrigerant as it cycles through the system. If the fan is malfunctioning (weak, not running, or intermittently running), it can impact cooling, especially at idle when the airflow from driving isn't present.
* Other Issues (less likely): While less common, issues with the expansion valve, orifice tube, or other components in the AC system could also contribute, but low refrigerant is the usual culprit for your specific scenario.
What to do:
1. Don't add refrigerant yourself: Adding refrigerant without fixing a leak is a waste of money and could further damage your system.
2. Take it to a qualified mechanic: A professional with AC diagnostic tools can:
* Check the refrigerant level.
* Identify and repair any leaks.
* Check the compressor clutch operation.
* Inspect the condenser fan.
* Evaluate the overall health of your AC system.
They'll use a pressure gauge to determine if the system is low on refrigerant and identify any other problems. They may also use a dye to help locate the leak.
Ignoring the problem will likely lead to further damage and a more expensive repair down the line. Get it checked out soon!
