To answer this question, you must understand; air conditioner capacities are rated primarily by their ability to transfer heat from the inside of your vehicle to the outside air. Your air conditioner may freeze up if it fails to pick up or transfer heat for any of the following reasons:
- Indoor and outdoor temperatures may be too cold (lack of heat).
- Evaporator air recirculation is possible due to poor or improper installation.
- Airflow obstructions:
- Dirty filters. Filters should be cleaned regularly.
- Supply air louvers may be shut off.
- Inadequate or damaged ducting (if so equipped).
- Dirty or plugged cooling (evaporator) coils.
- Low Fan Speeds (motor that is not pulling enough amps or airflow).
- Improper Operation: Setting the temperature on the thermostat so low the compressor does not cycle off and on. Running the compressor and low speed fan together may cause “freeze-up” conditions to accelerate.
Electrical problems, faulty thermostat, inoperative freeze thermistor.