Remember...you are dealing with a multi voltage set up. A 3 speed blower system will receive 3 different voltages to achieve the 3 different speeds. If you have too much resistance in the winding of the motor, it most likely won't run at the lower voltages. Your test of the motor with the Motor Cycle battery makes sense on the surface but you are hitting it with 12 volts head on and it is running. Now...the test is to read the RESISTANCE in OHMS in line with the motor at 12 volts. If the resistance is beyond specified numbers you may be getting a total drop out of the resisters trying to run that motor at any speed. In my situation, I was ignoring this thinking that my problem was upstream of the motor when all the while the motor was shot...even though it would run on the bench...until it got hot...then it would quit !!!
Get or find on line a section on troubleshooting this in a GM Shop Manual for your truck. There is a procedure for testing this system.
This is awesome advice. At the end of the day it is a blower motor thats bad. You have voltage and ground, motor should work. Thats all there is to it.
Now for the science. Like mentioned above, the motor has to much internal resistance which can be determined with an in line resistance test. When you placed 12v from a motor cycle battery to it, amps werent taken into consideration, that 12v is being pushed by probably at least 50 amps, more than enough to overcome the resistance in the motor. The maximum allowed amps on that circuit is probably 10 amps, not enough to turn this motor. Another hint is it took out to resistors, this is simply because that motor was constantly pulling to many amps. Measuring amperage in a circuit is a direct correlation to how much resistance is in the circuit. Gotta love laws.
At work I try to replace resistors and blowers together.
