Ender 3d s1 filament change at layer

I have a new ender 3d s1 and I tried using cura and a post script extension to stop the printer to do a filament change at a particular layer . The machine stops, ejects the filament from the extruder and then beeps…i load a new filament, the machine is cooling, when I press the button I assume to continue it starts to heat again. when it gets to setpoint it beeps and cools off again, repeated on and on… am i doing the change at layer wrong?, should I not have a broken filament sensor installed, or active? any help?