GMC Sierra 1500 HD air conditioning won't switch from vent to defrost, air only blows from vents on GMC Sierra 1500 HD

Some GMC Sierra 1500 HD owners report experiencing issues with their air conditioning system being stuck in the vent position, resulting in air only blowing from the vents instead of switching to defrost. This problem may stem from a malfunction in the temperature control, preventing the system from responding to the dash vent switch. Additionally, electrical climate control issues or a faulty air conditioning compressor could hinder the system's ability to switch modes. Some owners also report that refrigerant leaks, faulty compressors, or low refrigerant levels contribute to the AC system's malfunction, leading to inadequate cooling. Furthermore, problems with the drive belt, such as slippage or malfunction, can affect airflow and cooling efficiency. It is advisable for owners experiencing these issues to check these potential causes and seek professional assistance for accurate diagnosis and resolution.