When I was driving the bus home after we bought it, I had trouble with the defroster it would not heat up. I found the valves in the engine compartment and finally opened those and still the defroster would not blow warm or hot air. Two years later I finally found out why.......when pulling the old DD8v71n engine out I cut this line that went from the engine to the defroster, the valve in the picture is the valve that isolates the defroster. This metal slug was found in this line it is almost exactly the same size of the line. My guess is the mechanic who served this bus didn't much care for the driver, he never had heat for the drivers defroster! I guess the lesson learned here is don't mess with the mechanic!