Air conditioning unit for conditioning air (A M) aimed for an indoor environment, wherein said air conditioning unit comprises at least one housing structure and a refrigeration machine that includes at least one circuit (CF, CF 1, CF 2) configured to carry out a refrigeration cycle with a respective operating fluid, wherein said refrigeration circuit CF, CF 1, CF 2) comprises at least: - a first heat exchanger (11, 11-1, 11-2) of the air-liquid/gas type configured to carry out a heat exchange between said operating fluid and treated air (A M) destined for said indoor environment; - a second heat exchanger (12, 12-1, 12-2) of the air-liquid/gas type configured to carry out a heat exchange between said operating fluid and the external air (A E) of an outdoor environment; - a compressor (13, 13-1, 13-2) to increase the pressure of said fluid to a value characteristic of condensation and expansion means (14, 14-1, 14-2) to reduce the pressure of said operating fluid to a value characteristic of evaporation of said operating fluid, wherein said air conditioning unit further comprises - a first heat exchange section defining a first chamber in which said first heat exchanger (11, 11-1, 11-2) is housed, said first chamber comprising at least a first inlet communicating with said outdoor environment and at least one outlet suitable to be communicating with said indoor environment, said first section comprising first suction means for sucking at least a first flow of external air (A E) from said outdoor environment; - a second heat exchange section defining a second chamber at least partially delimited, with respect to said outdoor environment, by a first portion (12A, 12-1A, 12-2A) of said second heat exchanger (12, 12-1, 12-2), said second section comprising second suction means for sucking a second flow (F 2) of external air (A E) inside said second chamber through said first portion (12A, 12-1A, 12-2A) of said second heat exchanger (12, 12-1, 12-2), said second chamber comprising at least one discharge opening for the return of said second flow into said outdoor environment, characterized in that said air conditioning unit further comprises a third heat exchange section defining a third chamber separated from said first chamber and from said second chamber, said third chamber comprising at least a second inlet configured to be communicating, directly or indirectly, with said indoor environment, wherein said third section comprises third suction means configured for sucking into said third chamber a flow (F-A R) of return air (A R) coming from said indoor environment, wherein said third chamber is at least partially delimited, with respect to said outdoor environment, by a second portion (12B, 12-1B, 12-2B) of said second heat exchanger (12, 12-1, 12-2) so that said return air (A R) sucked into said third chamber is ejected directly into said outdoor environment through said second portion (12B, 12-1B, 12-2B) of said second heat exchanger (12, 12-1, 12-2) without passing through said second chamber. - a first heat exchanger (11, 11-1, 11-2) of the air-liquid/gas type configured to carry out a heat exchange between said operating fluid and treated air (A M) destined for said indoor environment; - a second heat exchanger (12, 12-1, 12-2) of the air-liquid/gas type configured to carry out a heat exchange between said operating fluid and the external air (A E) of an outdoor environment; - a compressor (13, 13-1, 13-2) to increase the pressure of said fluid to a value characteristic of condensation and expansion means (14, 14-1, 14-2) to reduce the pressure of said operating fluid to a value characteristic of evaporation of said operating fluid, wherein said air conditioning unit further comprises - a first heat exchange section defining a first chamber in which said first heat exchanger (11, 11-1, 11-2) is housed, said first chamber comprising at least a first inlet communicating with said outdoor environment and at least one outlet suitable to be communicating with said indoor environment, said first section comprising first suction means for sucking at least a first flow of external air (A E) from said outdoor environment; - a second heat exchange section defining a second chamber at least partially delimited, with respect to said outdoor environment, by a first portion (12A, 12-1A, 12-2A) of said second heat exchanger (12, 12-1, 12-2), said second section comprising second suction means for sucking a second flow (F 2) of external air (A E) inside said second chamber through said first portion (12A, 12-1A, 12-2A) of said second heat exchanger (12, 12-1, 12-2), said second chamber comprising at least one discharge opening for the return of said second flow into said outdoor environment,