There could be several reasons why your AC unit is not going lower than 75 degrees. Some common causes include:
Thermostat Calibration: The thermostat might not be calibrated correctly, causing it to misinterpret the actual room temperature. As a result, when you set it to 74, it may think the room is already cooler than it is and adjust back to 75.
Airflow Restrictions: Restricted airflow due to dirty filters, blocked vents, or obstructions around the unit can affect its ability to cool the room efficiently.
Size of the AC Unit: If the AC unit is undersized for the room, it might struggle to reach lower temperatures, especially during extremely hot weather.
Refrigerant Leaks: Low refrigerant levels can lead to reduced cooling capacity, making it difficult for the AC to achieve lower temperatures.
Outdoor Temperature: Some AC units have difficulty reaching lower temperatures during extremely hot weather, as they are designed to operate within a certain range.
Thermostat Location: If the thermostat is placed in a location affected by direct sunlight or drafts, it may not accurately reflect the room's overall temperature.
AC Unit Issues: There could be internal issues with the AC unit, such as a faulty compressor or sensor, that prevent it from functioning correctly.
To troubleshoot the issue, you can try the following steps:
Check the thermostat's calibration and make sure it is reading the room temperature accurately.
Ensure there are no obstructions or debris around the AC unit, and clean or replace the air filters if they are dirty.
Verify that the thermostat is not affected by external factors like sunlight or drafts.
Consider the outdoor temperature, as extremely hot weather might affect the AC unit's performance.
If none of these steps resolve the issue, it's best to call a professional HVAC technician to inspect and diagnose the problem with the AC unit. They can identify any internal issues and make the necessary repairs or adjustments.