The most appropriate reason should be the conduction of air.
Temperature could drop because of conduction, convection, and radiation. Conduction by direct contact, convection if the air move to the nenonate and radiation by electromagnet waves. If the neonates don't get blow up by the AC directly, the temperature drop would because of the contact with the air. In this condition, it is best to cover the patient with a blanket so the contact will be minimized.
The right answer is decreased nonshivering thermogenesis.
The increase in metabolism allows an increase in the production of heat. Newborns use their brown fat as a source of heat, it is a non shivering thermogenesis.
The second mechanism for increasing heat in humans is increased muscle tone and shivering, but in the newborn there is no chill.
