What's the reason when the car AC indicator light is on but the compressor doesn't start?
3 Answers
The reason why the car AC indicator light is on but the compressor doesn't start is due to compressor damage. The following describes the process of air conditioning refrigeration: 1. Compressor operation: When the car air conditioning is cooling, the compressor clutch will engage, at which time the engine drives the compressor to operate. During operation, the compressor continuously compresses the refrigerant and delivers it to the evaporator. 2. Refrigerant operation: The refrigerant continuously expands and absorbs heat in the evaporator, cooling the evaporator; the cooled evaporator then cools the air blown by the blower, allowing the car air conditioning vents to blow cold air.
I've encountered a similar issue before, and it's quite annoying. When the AC indicator light is on but the compressor doesn't start, the most common cause is the AC clutch not engaging—it could be a faulty clutch coil or poor wire connection. First, simply check if the AC fuse in the fuse box is blown. If you hear the relay clicking but the compressor doesn’t respond, the pressure switch might be the culprit. Too little refrigerant will trigger automatic protection to prevent startup. Also, check the belt in the engine bay to see if it’s loose or broken. When I dealt with it last time, I used a multimeter to test the voltage and found a short circuit causing insufficient power supply. In the end, replacing the wiring connector fixed it. If you don’t have the tools, don’t force it—take it to a professional repair shop for a quick diagnosis. Regularly cleaning the AC filter can also reduce such issues and ensure reliable AC performance in the summer.
From my experience, when the AC light is on but the compressor isn't running, it often points to several key component failures. The indicator light working normally shows the control system is activated, but the compressor itself may be stuck or the clutch may be worn out. In terms of electrical circuits, burnt relay contacts can interrupt the signal, and the pressure sensor detecting refrigerant pressure that's too low or high can also prevent startup. This is more common in hot weather due to increased system load. If you can check yourself, pop the hood and listen for any unusual sounds from the compressor while also inspecting if the fuses are intact. I recommend not delaying too long - a non-functioning compressor reduces cooling efficiency, increases battery load, and raises fuel consumption. Have a technician perform a comprehensive inspection with professional equipment as soon as possible, including testing whether the ECU output signals are correct.