From what you are describing, you have one or two things that could be going on, but odds are it is the switch that is causing the issue.
One way to test this will be to connect the 2 wires in the back of the actual switch. This will complete the circuit, which the pull pin should be doing, and will tell you immediately if it is the issue. If the brakes are now working properly, you will need to replace it with the Replacement Breakaway Switch # RM-650898. The removal of the pull pin can... view full answer...
For your Dometic Duo-Therm, you can use the:
-Replacement Shroud for Dometic Duo-Therm RV Air Conditioner # DMC69FR for a replacement shroud. view full answer...