Several factors could contribute to your AC not cooling properly. Common issues include dirty air filters, blocked or dirty condenser coils, refrigerant leaks, frozen evaporator coils, malfunctioning components like the compressor or fan motor, incorrect thermostat settings, or inadequate insulation. Additionally, undersized AC units may struggle to cool larger spaces effectively. Professional diagnosis is recommended to identify the specific problem affecting your AC's performance and ensure proper repair or maintenance.