Dodge Van Blower Motor Blows Medium for HI

This seems to be my summer for blower motor issues, having just dealt with one on my daughter’s car ( http://act… ). This time, its the 1992 Dodge B350 van (5.9L v8, 206,000 miles).

On this one, the front blower motor blows OK on the LO and MED settings. But when I move the switch from MED to HI, the blower motor still blows at MED. There is no difference between MED output and HI at all, either in terms of the actual amount of air coming out, or the sound of the motor itself. Going to HI is as if it never got switched out of MED.

Here is a diagram of the circuit.


Anyway, my immediate suspicion is the switch. I also thought it would make sense to run a fused humper straight from the battery to the blower to see if it blows HI that way. I am kind of guessing here, since the factory service manual for the Dodge van has circuit diagrams, but no diagnostic test procedures.

As usual, any input is greatly appreciated, and I’ll post back results!

Probably the switch. Does she really need hi speed?

I agree that the blower speed switch or the wiring to it are the most likely suspects for this.
Yes, running a fused jumper from the battery would be a good test. (I don’t think that a fused humper would do any good though.)

Thx. I meant to say jumper, but my bad typing skills got the better of me.

Yes, its a big 15-passenger van (untinted wondows), and I need all the blower output I can get to keep it cool.

Using a voltmeter check to see if there is a voltage drop (voltage drop across the switch contacts would mean a bad switch) across terminals A and B of the AC Heater Vacuum switch while it is in the heat position and the speed switch is set to HIGH. If there is no voltage drop there then check the voltage on terminal B with the meter common probe tied to a good ground. There should be over 12 volts there if things are ok with that switch. You can check the speed switch also if the other switch is ok.

I’ve had to replace the resister bank (located behind the glove box) twice on my wifes van. It shows no signs of failure, but when it’s replaced the fan works on all speeds. I’ve been told that the reason it fails is because the blower motor is starting to fail.