If your car's air conditioning (AC) continues to cool below the set temperature and does not shut off, it could be due to a few possible reasons:
Faulty thermostat: The thermostat is responsible for sensing the temperature inside the vehicle and signaling the AC system to turn on or off. If the thermostat is faulty or misreading the temperature, it may not accurately shut off the AC when the desired temperature is reached.
Sensor issues: Some cars have additional sensors to monitor the cabin temperature or other factors that affect the AC operation. If these sensors are malfunctioning or giving incorrect readings, it can result in the AC cooling beyond the set point and not shutting off.
System leak: If there is a refrigerant leak in the AC system, it can cause the system to cool excessively. Insufficient refrigerant levels can prevent the AC from cycling off properly, as it tries to compensate for the low refrigerant by continuing to cool.
Control module or electrical problems: Issues with the control module or electrical components that regulate the AC system's operation can lead to irregular behavior, such as the AC not shutting off at the desired temperature.
To resolve this issue, it is recommended to have your car's AC system inspected by a qualified technician. They can diagnose the specific cause of the problem and perform the necessary repairs or adjustments to ensure that your AC functions correctly and shuts off at the desired temperature.