Why does the car air conditioner turn on and off intermittently?
2 Answers
The compressor turns on and off intermittently because it automatically starts or stops based on the set temperature, rather than running continuously. This intermittent operation is a protective phenomenon of the compressor, representing the recovery time of the compressor's thermal protector. Typically, this takes only a dozen to several dozen minutes, but these values may change after prolonged use of the compressor. The main reasons for this protection are threefold: 1. Lack of refrigerant: Insufficient refrigerant in the system causes the compressor's exhaust temperature to trigger thermal protection. Even if there are white bubbles at the needle point, it only indicates the presence of refrigerant in the system, but the amount and whether there is a shortage cannot be determined. 2. High exhaust pressure: Excessive exhaust pressure from the compressor increases the operating current, leading to current thermal protection. There are many possible causes, such as poor ventilation of the external heat exchanger, a dirty or clogged heat exchanger, or a faulty external fan motor, any of which could result in this situation. 3. Faulty thermal protector: A malfunctioning thermal protector in the compressor can also cause this issue, though this situation is more troublesome and usually requires replacing the compressor.
Last time, the air conditioning kept turning off shortly after starting. I think this is quite common. Having repaired cars for over a decade, the usual causes are issues with the compressor clutch or insufficient refrigerant. For example, poor clutch engagement can make the AC shut off after just a minute or two, or when refrigerant is low, the system pressure drops too much and triggers the protection mechanism. It could also be a faulty AC control module, where the sensor misreports temperature, causing it to cycle on and off. If the evaporator freezes or the filter gets completely clogged, it can block airflow and force a shutdown. I remember one time I checked a car with a pressure gauge to measure refrigerant levels and found the issue—replacing the filter improved it. Car owners shouldn’t delay; it’s best to visit a repair shop early to avoid compressor damage and higher costs.
