* Low refrigerant: This is the most frequent cause. If the system is low on refrigerant, the remaining refrigerant can't absorb enough heat to effectively cool the air, causing ice to form on the evaporator coil. Leaks are the typical reason for low refrigerant. A leak detection is necessary to find and fix the source.
* Restricted airflow: Several things can block or reduce airflow over the evaporator:
* Clogged cabin air filter: A dirty filter severely restricts airflow. This is an easy and inexpensive check.
* Blocked evaporator fins: Dust, debris, or leaves can accumulate on the evaporator fins, impeding airflow. This often requires professional cleaning.
* Problems with the blower motor or its resistor: A weak or failing blower motor won't move enough air, or the resistor might be preventing the fan from operating at higher speeds.
* Malfunctioning blend door: This door controls the mix of hot and cold air. If it's stuck, it might restrict airflow to the evaporator.
* Frozen expansion valve or orifice tube: These components regulate the flow of refrigerant. If either is frozen or clogged, it prevents proper refrigerant flow and leads to icing. This is less common but possible.
* Faulty compressor clutch: If the compressor isn't cycling on and off correctly, it can lead to overcooling and freezing.
* Refrigerant charge issue: Even with the correct amount of refrigerant, an improper charge (too much or too little, or an incorrect type) can result in freezing. This points to a need for a professional AC service.
Troubleshooting Steps (in order of easiest to hardest):
1. Check the cabin air filter: This is the first and easiest thing to check. Replace it if it's dirty.
2. Check blower motor speed: Make sure the fan is running at a reasonable speed. If it's weak, there might be a problem with the blower motor or its resistor.
3. Inspect for leaks: Look carefully for any signs of refrigerant leaks (oil stains, hissing sounds). This is best done by a professional with leak detection equipment.
4. Have a professional recharge/inspect the system: A qualified mechanic can check the refrigerant level, pressure, and look for leaks using specialized equipment. They can also properly diagnose more complex issues.
Do not attempt to add refrigerant yourself without proper equipment and training. Improperly charging the system can damage components and lead to further problems. It's best to leave this to a professional.
