Blower motor - multi speed

"97 S10 Blazer" - The blower motor won't function on the top speed (4th click) of the rotary switch. I don't have a very good wiring diagram, does anyone have an idea why it won't function? Is there a relay involved only for the highest speed? About the same time the rear wiper quit also. I purchased a used wiper motor and switch assembly which won't work either. Running power to the wiper motor directly does work though, on both units, so I now have a spare. If anyone has a clue or better yet could e-mail me a copy of a diagram of the electrical systems involved in the problems stated above it would be greatly appreciated. Thanks in advance! ([email protected])

ok here is your basic heater circuit...it contains 1) a blower motor 2) a rheostat 3) a switch 4) and some wiring. A rheostat is a variable resistor, it varies the amount of current that is allowed to pass through to the blower motor. When you switch the heater to high, it allows all 12 volts to pass through it, when you go down a notch it allows only say 10 volts to pass through, therefore slowing the motor down, and so on. So in order for the rheostat to be at fault it would have to kill all four settings if the highest one is broken, meaning it is possible to not have the first, second, and third setting work and still have the four work....but not the opposite way around. Ok, so i suspect it is in the switch itself, or possibly the blower motor, does it make any wierd noises? squeeling? if yes then your motor is dying, if no then i think it is the switch. here is a good diagram of a rheostat (or variable resistor)

http://www.ame.ch/elektrglf/rheostat.gif

ignore all the writing cause i don't know the language. basically you see the wire winding going left to right....this is where the power goes through, 12 volts in. The slider at the top is the part that goes to the blower motor. Let's say the power enters on the left side and exits the right. When the slider is on the left side it is getting all 12 volts....when the slider is in the middle it is getting (let's say) 10 volts and when the slider is on the right it is only getting like 8 volts or so. Ok so you get the idea, basically what happens is the further away the slider gets the less power it gets...the rheostat transforms the electricity into heat energy, therefore reducing power. Man i think i went a little to far here....now you know how a rheostat works, you see how if your getting all the lower settings then the wire must be good all the way through, if your not getting high setting, or full power the wire is burnt or damaged and therefore the other settings cannot work. Ok so this supports my theory of your switch being shot. I really hope your still awake, hope this helped.

Thanks for the response Fox_Rocks. I understand how a rheostat (a.k.a. variable resistor) functions thats why I came to the conclusion that there must be a relay involved with the highest setting. If all settings were through the rehostat then as you stated, you lose one you lose them all since it would mean there is an open in the winding. I'll have to pull the switch assembly to check if theres a lead out on the high setting side that would be the trigger for the relay. I've got the Haynes manual but I can't seem to locate the blower /heater schematic in it, and I don't feel like dropping $110 on the Helms service manual, although these are great reference material. I got the one for my 91 Firebird Formula and the wiring diagrams are outstanding. Thanks again.

no prob. sorry about geting carried away with detail, i do that sometimes.

Not real sure on the 98 but usually a relay on the AC box under the hood and the high speed runs on a fusable wire. If you can locate that relay check for voltage on the big wire coming to the relay.