What are the reasons for a car's air conditioning suddenly not working?

[OGenevieve]

There are several reasons why a car's air conditioning may suddenly stop working: 1. Engine control logic error: Unable to receive the signal to turn on the air conditioning. When it cannot determine whether the air conditioning is on, the engine control unit (ECU) may mistakenly perceive it as a temporary high load and attempt to compensate by increasing the engine speed to offset the resistance at idle. When the engine speed drops, it cannot handle the load of the air conditioning compressor, causing the speed to increase again. 2. Air conditioning control circuit error: Unable to send the signal to turn on the air conditioning. Since the ECU cannot determine the air conditioning's status, it continuously adjusts the idle speed, resulting in unstable idling. 3. Air conditioning circuit malfunction: Causes the air conditioning to work intermittently. When the air conditioning is not working, the compressor belt runs without load, so it does not affect the engine load.