Got an emergency call this morning from Ropesville - AC completely dead during this heat wave! Arrived to find a Trane XR13 system with zero response. Quick check showed the disconnect was fine but no power at the air handler. Traced the problem to a completely fried control board (could actually see burn marks!) plus a blown 3-amp fuse on the furnace control. Replaced both components and while I was at it, noticed the contactors were pretty worn. Went ahead and replaced those too since they were on their last legs. Also found a mouse nest near the control board that probably caused the short - cleaned that out completely and sealed the access point they were using. System fired right up after repairs! Everything's running perfectly now with proper voltage readings all around. Homeowner was so relieved to have cool air again. Left them with some preventative maintenance tips and scheduled their next regular service.