in dash temperature control
 

After reading several posts about monovalves and temperature control sensors, can someone answer this question for me? The monovalve seems ok cause when I disconnected the electrical plug I get good constant heat whether the setting is at 18C or 26C. (My car is running at idle). However when I disconnect the above dash temperature sensor, the heat turns cold. Is this supossed to happen or is the sensor bad?:confused: