Chevrolet Repair: Electrical Ground feed, resistor pack, resistor packs

Question
I should have said that this motor works on high speed only and won't run on the other speeds when I turn the control.It will blow the resistor after a while
Is that possible with a one speed motor?
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Followup To

Question -
Hi Van

My question...
In testing a circuit, in this case a blower for the heater I am confused.

I am using a regular test light(non powered) and when I test the ground side of the blower connector the light lights up. If I unplug the circuit and test the connector before the blower , the light stays off.
To me this means I am getting feed back to ground in the blower motor..correct? So that would mean either a bad ground at the blower motor or the motor itsef? I have also disconnected the blower from the whole circuit, powered it up with 12 volts and still get a light to ground,
This is a one speed motor with a dash switch that changes the speed.
I have changed the dash switch, blower resister(which has blown twice) am i right in thinking the blower motor?
Thanks
Dennis
Answer -
Hi Dennis,
If you are getting the light to light with the clip of the light connected to battery neg, and the probe on the blower motor ground wire, then you have a bad ground.
If you have power going to the blower, and use a jumper wire from the other terminal to battery ground, it should run at full speed.
Van

Answer
Hello Dennis,
To the best of my knowledge, ALL motors on vehicles are One speed. The speed is varried by voltage adjustments, ie resistor packs, or rheostats(which are just infinitely variable resistors).
Even direction of rotation can be changed on most of them by reversing the hot and ground connections.
Now on your question, I don't see a vehicle type, but that is irrelevent, other than it might have me tell you where to find a couple things.
So I wonder if you are blowing the resistor pack, or are we maybe meaning the relay?
Your dash mounted speed selector switch just selects which terminal on the resistor pack to send battery voltage to. The resistor pack is mounted in the blower air flow duct for a reason. That reason is because it gets HOT when it is doing its job, and the air flow helps cool it.
The more resisting it does, like for LOW speed, the hotter it gets.
Two things will shorten its life.
No air flow while it is working, due to the blower not blowing, or a bad to dead short in the blower motor, which will cause the motor to overheat, run slower or not at all, and draw excess amperage, all of which will be detrimental to the resistor.
On high speed, the resistor is completely bypassed, directing full battery voltage to the blower motor.

Another problem in those switch circuits is LOOSE connections, which cause resistance, and heat, usually at the connection, which in Dodge pickups usually showed up at the fan speed switch during long air conditioning periods. The switch and connector housing would actually melt.
So make sure all your connections, including the blower ground wire, are clean and tight.
Also, check the ground wire from the firewall to the engine block for clean and tight.

Hope some help here. Good luck,
Van