What Causes the Whistling Sound in a Car's AC Expansion Valve?

[LaMaverick]

An abnormal noise from the car's AC expansion valve indicates a blockage in the valve. Here are the relevant explanations: 1. Internal AC noise: There is an abnormal sound in the air ducts. If the AC filter has not been replaced for a long time, there may be foreign objects like leaves in the ducts. These can be removed at a repair shop using high-pressure air. 2. Noise from refrigerant evaporation and expansion: If there is air or moisture in the refrigerant within the AC compressor, it can cause abnormal sounds during refrigerant evaporation and expansion. The solution is to evacuate and replace the refrigerant. If the noise recurs after some time and is located inside the dashboard, the desiccant bottle's efficiency may have decreased. If the noise persists after refrigerant replacement and is near the compressor, there is a higher likelihood of internal mechanical damage to the compressor.