What are the reasons for no cold air from the car air conditioner?

[StNoah]

Car air conditioner not blowing cold air may be caused by: 1. Insufficient refrigerant; 2. Damaged air conditioner flap; 3. Dirty condenser; 4. Faulty air conditioner compressor, throttle valve or expansion valve. Functions of car air conditioning: 1. Achieves cooling effect through continuous phase change cycle of refrigerant; 2. Removes dust, odors, smoke and toxic gases from the car interior to freshen the air, and humidifies the cabin air to increase relative humidity; 3. Uses engine coolant, waste heat or heat generated by burner combustion as heat source, which is then heated by the heater and blown into the cabin by the blower to raise outlet air temperature for heating purposes; 4. Draws in fresh outside air for ventilation and air exchange, also effectively preventing windshield fogging.