Abstract: Unit for conditioning and distributing air in the passenger compartment of a motor vehicle with front and rear seats, comprising: a cold air flow collection chamber (26) downstream to the evaporator (14) with reference to the direction of movement of the air flow, an air flow heating unit (18, 20), a hot air flow collection chamber (28), arranged downstream to the heating unit (18, 20), a longitudinal separation wall splitting the front seat unit into two separate areas for the driver and the front seat passenger, respectively, a rear seat air flow mixing chamber (54) communicating with the hot flow collection chamber (28) and a cold flow collection channel (60) extending under said heating unit (18, 20) and communicating with a first end of said cold flow collection chamber (26) and with a second end of the rear seat mixing chamber (54).