The most common cause of a double shade with a 19-inch, 3/4-inch tube not stopping when pulled down is a worn or faulty internal spring mechanism. To fix this, you should replace the replacement spring designed for your tube diameter. Elkhart RV Parts offers replacement springs specifically for 3/4" roller tubes, such as the Irvine replacement springs suitable for Valu-Line RV roller shades. Adjusting the tension wheel on the roller tube may help, but typically the spring needs replacing. If you have already replaced springs multiple times and still face issues, the problem might be with the auto stop end or another internal component, and further technician evaluation would be recommended. You can order the appropriate springs from Elkhart RV Parts and expect fast shipping to restore proper function to your shade.