Hi Keith , Arc cannot increase a current , basic physics of it . The heat loss etc or arc is in series with motor power , so that is a voltage drop like the speed resistor which also then drops the current . Like speed resistor. So the current in the fuse drops with bad contacts , which also burn . Motor slows . I do not question what you see but explanation of blown fuse is not a contact arc . AC induction motors draw more current on low volts might be where you get this ? But that is not here .
As a guess , some intermittant problem in blower motor ( sticks mechanically at start ( bearings) or burned brushes ) or as Don said a short to ground . ( possibly erratic) The only way current can rise above normal is shorted coils or stalled motor or a short to Ground in a control switch or wire . Someone said clutch is on separate fuse , and my comment on clutch with this fuse might be wrong .. As Don said various control schemes over the years . Follow that 25-30A wire on FS diagram , look at every place it goes . Put ammeter at motor see what it draws or if it jumps around .
Also hi currents in SAE 25 or 30 fuses can melt the fuse if clips are loose or corroded and bending them generally makes it worse . This usually takes 20 sec or more . I have had to wire in an in line fuse in every pre 1990 Dodge Truck heater fan I ever owned , end of the fuse clips melt loose . 300F heater switch too .
If it blows instantly = usually a short .. That can come and go . If motor jammed for 5 sec maybe it blows . When the contacts close .
I think it is the repetitive motor start up process that you are eliminating by shorting the contact ?
All this is from very far away but an ammeter ( or the one on your dash ) is next . Watch if it jumps way high at start . Once free and running the current will drop to normal . But if stays up a few seconds motor Is having a hard time getting going . That would blow fuse randomly at start up of fan ?
Hope this helps !
Sent from my iPhone
On Aug 14, 2016, at 1:55 AM, Keith Boonstra <kboonstra.zeegroup@xxxxxxxxx> wrote:
Posted by: John Grady <jkg@xxxxxxxxxxxxxxxxx>
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