2006 Volvo S40 Constant hot air blowing

With 16k miles you may still be under warranty depending on the delivery date of the vehicle. The most likely problem with the A/C system going out is a worn compressor clutch but you would need to have it diagnosed to see if that is the problem. Other problems could be low freon, a bad pressure switch, bad relay, bad climate control unit, or the engine control module not supplying the ground? The compressor clutch you can have the clearance measured. Should be between 0.3mm - 0.5mm anything greater then that then you need to replace the clutch on the compressor.