Multiplus II 12/129 Inverter stopped working

When traveling I noticed that we left the A/C unit on and when we shut it down, the inverter shut off and stopped working. I found the disconnect switch betweent the batteries and inverter had melted. I replaced the switch but the inverter is still not operating. It appears as though the charger and pass through functions are working. Is there a fuse that could have blown (I do have a 400 amp type T fuse in the battery circuit. it did not blow) or a relay that has failed. the unit is 18 months old. any suggestions,?