I think the question I get asked the most is, well I dunno know, it happens a lot, enough that I would remark on it – a lot of people come up to me and they say “How do I know if my flow sensor is positioned within spec?“
My answer’s always the same, I say: “Listen. Luckily we don’t have to go all the way back to the Civil War to answer this…” ¹
The truth is, most never check, but here’s a quick easy way to ensure your Minneapolis fan’s flow sensor’s positioned properly in the field. So easy in fact that you’ll do it every time!
The spec for a Model 3 fan is between 3/16″ (4.7mm) and 5/16″ (7.9mm). See page 58 and 59 of the Operation Manual.
Lay the fan flat so flow sensor hub is up. Using the fan frame’s cross bar, use a measuring tape, simply measure the gap!
Easy as pie: slap your cross bar on the back face of the fan carcass so it spans the fan housing and measure the gap. I used my grandfather’s T-square for the picture above, but you can use your measuring tape!
And the reading is 2/8″ AKA 4/16″ or 1/4″! We’re in the house!
If your fan is not in spec, the fix is super easy, you’ll have to loosen a bolt and move the motor in the mounting bracket till its within. You can learn more about it in this article I wrote a while back for Homer Energy magazine called Pimp My Blower Door: A blower door make-over.
¹ Sorry for the cheesy homage to Tom Waits.