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blower motor

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SSChevy:
i have a 78 T/A auto with A/C  (and T-Tops, just sayin, lol). I bought "ALL" A/C related NEW harnesses from American Autowire and thought that would get my Blower Motor spinning, it hasn't yet worked. Q. shouldn't the new motor I bought spin, when I jump it to a 12vdc source while grounding the case? It wont spin this is my 3rd blower motor. I just want to know I have a good motor before I expect it to work with the cars system.

YouTube channel is: ""Jeff's real estate diary"", look at my install here, ""1978 Trans Am A/C wiring harness, every component location show by name"".

5th T/A:
12 volts to the spade lug connection on the blower and grounding the blower housing will give max blower speed. Without even installing the new blower motor you could do the same test with a set of jumper cables.

Hard to believe you had three bad blower motors.

SSChevy:
thank you 5th T/A I put 12vdc on the new/3rd motor and it spun right up. I also did 12vdc to the motor in the car but no spin took place.
Tomorrow I'm going to Ground the one in the car better and see if that will make it spin.
If it still doesn't spin I'll put the new motor in and hope it gives three speeds and goes off as asked by the Fan switch on the dash.
Thanks for the reassurance that direct voltage will make it spin, I thought it needed a capacitor. Now I know it doesn't.
I will post a YouTube video showing the whole diagnoses resolve. :D

5th T/A:
You could be on the right track by not having a good ground. This can easily be checked with a DVM. Measuring from the positive battery lead to you blower ground will read approximately 12.5 volts with engine not running. If your meter says 0 VDC, you don't have a good ground.

If this is an AC car it will have four blower speeds. The lower three speeds get their power from the blower switch that connects to a resister pack that is installed in and cooled by the (suitcase) evaporator housing. The resistors reduce the voltage to the blower causing it to run at reduced speeds. High/max speed comes from a relay on top of the evaporator housing. While the relay is energized by the blower switch all the current comes from the alternator output post, essentially the same electrically as the battery. These relays were famous for failing, but usually the symptom is no high blower speed.

Wallington:
I'll check out the YT Diary later, cheers.

Not sure if it applies here if fully replaced with new harness which is meant to be the same, but often when guys remove their A/C gear then complain the fan doesn't work is because the ground wire for the fan is in the harness they just removed, and mounts on the compressor bracket, they also just removed.

Having said that, and not knowing much else, check that this ground wire exists, normally mounts on locating bolt for compressor in brackets. Also, if A/C has been replaced or 'upgraded', check that these aren't painted up or alloy, or a bad grounding. If you find the wire, run another wire off it to a better ground just to test. Otherwise, can start looking at the positive feed side of things, and if fan is dead on all speeds. High speed is full direct power and bypasses the resistors. If you have one and not the other you can pinpoint something, just like you can pinpoint other issues if no power there at all. That is an easy access area, before you try testing power at fan switch. Do you know when it last ran, prior to any changes?

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