What Causes the Whistling Noise in a Car's Air Conditioning Expansion Valve?
2 Answers
An abnormal noise from a car's air conditioning expansion valve indicates that the expansion valve is clogged. A faulty expansion valve and a blocked system exhibit similar symptoms, such as poor cooling or heating performance, and in severe cases, no cooling or heating at all. Here are several types of internal noises in a car's air conditioning system: 1. A water-flow-like sound from the chassis: When the air conditioning is turned on, a noise resembling flowing water is heard from the chassis. This is the expansion valve operating normally. 2. Abnormal noise in the air duct: The air filter has not been replaced for a long time, or there are foreign objects like leaves in the air duct. 3. Air in the compressor: The presence of air or moisture in the refrigerant of the air conditioning compressor can cause abnormal noises during refrigerant evaporation and expansion.
That time on a long drive, I suddenly heard the AC whistling like crazy, which scared me so much I pulled over immediately. The mechanic took one look and said the expansion valve was toast, with refrigerant rushing through a narrow gap creating that high-pitched noise. Either the filter screen was clogged into a funnel shape, or the valve spring snapped causing opening/closing failure. Even worse—the last guy who topped up the refrigerant overfilled it by accident, making the pressure spike and scream. Now I know you gotta replace the dryer bag regularly, as moisture getting in can freeze and jam the valve. These days, whenever I hear the AC start singing, I instantly turn it off, terrified it might suddenly explode and spray frozen oil in my face.
