Abstract: A fiber tuft processing line for processing fiber tufts preparatory to spinning, includes a plurality of fiber processing machines, fiber tuft conveying ducts serially connecting the machines, a blower generating a fiber tuft conveying air stream flowing in the fiber tuft conveying ducts, and an air conditioning system for supplying conditioned air to the machines of the fiber processing line. The air conditioning system includes an air conditioner; conditioned air conveying ducts extending from an output of the air conditioner to the machines; a humidity sensor and temperature sensor for responding to humidity and temperature conditions in the processing line; and a regulator for operatively connecting the humdiity sensor and the temperature sensor with the air conditioner. The humidity sensor is arranged to respond directly to the humidity of the fiber tufts in the processing line.