I had one speed "missing" on my blower, and it turned out to be the dash switch. In my case, speeds 2 and 3 were the same--but the blower operated in both positions. As I understand, this is a fairly common problem.
The blower resistor (at least on my 2008) is accessed from the engine bay, after pulling the battery. Unrelatedly, I checked mine recently but my problem turned out to be a dead motor (brushes were completely worn out).
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2011 Ford E350 EB Quigley 4x4 'PUPLGUK' | V10 Gas | Opt Overland Pop Top | GBS LiFeMnPO4 100Ah
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