The blower motor on my box van started to only work on high position on the dash, and at that time all the gauges(oil, volts, gas, water temp) on the dash would slowly goto there maxed out position. Then about 2 months later I had nothing at all, the fan would not turn on. I replaced the switch in the dash and, then I probed the leads to the blower, nothing at all. Any suggestions, thanks Matt.

 

The different speeds are controlled by a resistance unit mounted on the evaperator case near the blower.It has about 5 wires with one of them going directly to the blower hot lead.Each other wire is the signal from the dash switch,depending on the selected position.If no juice is available anywhere,you have a blown fuse or relay!Consult the owners manual for location and ratings.For the gauges,you are probably having ground trouble if they all go way up for no apparent reason.You might have a ground problem with the blower also.
Phillip

 

Had a similar problem, try shorting from the battery to the blower, and the blower to ground. If it run's it's not the motor.
If you have to replace the blower motor - make sure you get the pos and neg correct, or it runs, but only pushes a little air. The friend who replaced mine wired it up backwards, and ended up didling around for many hours (over the span of a month or so) checking out all the relays, pulling the dash etc. even though I suggested immediately he check the wiring to see if it was reversed.