An HVAC module, comprising: a housing defining an air inlet, a front zone air outlet, and a rear zone air outlet; an evaporator disposed within the housing downstream of the air inlet; a heater disposed within the housing downstream of the evaporator; a cold air chamber downstream of the evaporator defined in the housing between the evaporator and the heater, the cold air chamber having a first pressure (P ev); a hot air chamber downstream of the heater defined in the housing between the heater and a first interior surface of the housing, the hot air chamber having a second pressure (P htr) quantitatively lower than the first pressure (P ev) of the cold air chamber, the hot air chamber being in fluid communication with a rear zone mixing chamber defined by the housing, the rear zone mixing chamber having a third pressure (P mix) and being in fluid communication with the rear zone air outlet; a blend valve disposed in the rear zone mixing chamber; a cold air stream path defined by a second interior surface of the housing and an interior partition in the housing, the cold air stream path extending from the cold air chamber to the rear zone mixing chamber; and a control valve disposed in the housing between the cold air chamber and the rear zone mixing camber, the control valve configured to selectively control a release of cold air from the cold air chamber along the cold air stream path into the rear zone mixing chamber so as to control backflow of cold air into the hot air chamber; wherein the blend valve is a rear zone blend valve disposed at an entrance of the rear zone mixing chamber, wherein the rear zone blend valve is configured to selectively direct air flow from the cold air stream and the hot air chamber to the rear zone air outlet; characterized in that the module further comprises a control device configured and/or programmed to perform a method of controlling a backflow of cold air into the hot air chamber according to any one of claims 9 to 13. a housing defining an air inlet, a front zone air outlet, and a rear zone air outlet; an evaporator disposed within the housing downstream of the air inlet; a heater disposed within the housing downstream of the evaporator; a cold air chamber downstream of the evaporator defined in the housing between the evaporator and the heater, the cold air chamber having a first pressure (P ev); a hot air chamber downstream of the heater defined in the housing between the heater and a first interior surface of the housing, the hot air chamber having a second pressure (P htr) quantitatively lower than the first pressure (P ev) of the cold air chamber, the hot air chamber being in fluid communication with a rear zone mixing chamber defined by the housing, the rear zone mixing chamber having a third pressure (P mix) and being in fluid communication with the rear zone air outlet; a blend valve disposed in the rear zone mixing chamber; a cold air stream path defined by a second interior surface of the housing and an interior partition in the housing, the cold air stream path extending from the cold air chamber to the rear zone mixing chamber; and a control valve disposed in the housing between the cold air chamber and the rear zone mixing camber, the control valve configured to selectively control a release of cold air from the cold air chamber along the cold air stream path into the rear zone mixing chamber so as to control backflow of cold air into the hot air chamber; wherein the blend valve is a rear zone blend valve disposed at an entrance of the rear zone mixing chamber, wherein the rear zone blend valve is configured to selectively direct air flow from the cold air stream and the hot air chamber to the rear zone air outlet; characterized in that the module further comprises a control device configured and/or programmed to perform a method of controlling a backflow of cold air into the hot air chamber according to any one of claims 9 to 13.