A system for controlling negative pressure therapy with fluid instillation therapy using properties of fluids at a tissue site, the system comprising: a tissue interface (108, 408) disposed at a tissue site and coupled to a source of instillation fluid; and a dressing interface (107, 400) coupling a source of negative-pressure to the tissue interface (108, 408), the dressing interface (107, 400) comprising: a housing having a therapy cavity including an opening disposed in fluid communication with the tissue interface (108, 408), and a negative-pressure port fluidly coupling the therapy cavity to the source of negative-pressure; a pressure sensor (120, 416) mounted to the housing in fluid communication with the therapy cavity and configured to sense the pressure of fluids adjacent the tissue interface (108, 408) during instillation of liquids to the tissue interface (108, 408); a humidity sensor mounted to the housing in fluid communication with the therapy cavity and configured to sense the humidity of fluids adjacent the tissue interface (108, 408) during instillation of liquids to the tissue interface (108, 408); a temperature sensor mounted to the housing in fluid communication with the therapy cavity and configured to sense the temperature of fluids adjacent the tissue interface (108, 408) during instillation of liquids to the tissue interface (108, 408); and a processing element electrically coupled to the pressure sensor (120, 416), the humidity sensor, and the temperature sensor for receiving property signals indicative of the pressure, humidity, and temperature, the processing element determining flow characteristics of the system, wherein the flow characteristics comprise at least one of a blockage, a fluid leak, and an air leak. a tissue interface (108, 408) disposed at a tissue site and coupled to a source of instillation fluid; and a dressing interface (107, 400) coupling a source of negative-pressure to the tissue interface (108, 408), the dressing interface (107, 400) comprising: a housing having a therapy cavity including an opening disposed in fluid communication with the tissue interface (108, 408), and a negative-pressure port fluidly coupling the therapy cavity to the source of negative-pressure; a pressure sensor (120, 416) mounted to the housing in fluid communication with the therapy cavity and configured to sense the pressure of fluids adjacent the tissue interface (108, 408) during instillation of liquids to the tissue interface (108, 408); a humidity sensor mounted to the housing in fluid communication with the therapy cavity and configured to sense the humidity of fluids adjacent the tissue interface (108, 408) during instillation of liquids to the tissue interface (108, 408); a temperature sensor mounted to the housing in fluid communication with the therapy cavity and configured to sense the temperature of fluids adjacent the tissue interface (108, 408) during instillation of liquids to the tissue interface (108, 408); and a processing element electrically coupled to the pressure sensor (120, 416), the humidity sensor, and the temperature sensor for receiving property signals indicative of the pressure, humidity, and temperature, the processing element determining flow characteristics of the system, wherein the flow characteristics comprise at least one of a blockage, a fluid leak, and an air leak. a housing having a therapy cavity including an opening disposed in fluid communication with the tissue interface (108, 408), and a negative-pressure port fluidly coupling the therapy cavity to the source of negative-pressure; a pressure sensor (120, 416) mounted to the housing in fluid communication with the therapy cavity and configured to sense the pressure of fluids adjacent the tissue interface (108, 408) during instillation of liquids to the tissue interface (108, 408); a humidity sensor mounted to the housing in fluid communication with the therapy cavity and configured to sense the humidity of fluids adjacent the tissue interface (108, 408) during instillation of liquids to the tissue interface (108, 408); a temperature sensor mounted to the housing in fluid communication with the therapy cavity and configured to sense the temperature of fluids adjacent the tissue interface (108, 408) during instillation of liquids to the tissue interface (108, 408); and a processing element electrically coupled to the pressure sensor (120, 416), the humidity sensor, and the temperature sensor for receiving property signals indicative of the pressure, humidity, and temperature, the processing element determining flow characteristics of the system, wherein the flow characteristics comprise at least one of a blockage, a fluid leak, and an air leak.