I am not familiar with a Xantrex 2000/4000, but if like all the other Xantrex units I have worked on.....
Should be VERY simple to trace:
Shore power and generator should "meet" at the ATS.
From ATS both sources go to the RV main breaker box.
There should be a breaker on the main breaker box going to the inverter/charger.
And when the inverter/charger "sees" 120 VAC from that source, it does TWO things: charges batteries and through its built-in transfer switch, changes from "inverted power" to that supplied from the main breaker box.
If the charger section of the inverter/charger is working (meaning that 120 VAC is getting to the inverter, then "first suspect" is the transfer switch in the inverter/charger.
