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Old 05-06-2012, 11:29 PM
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Vampiric buyer motor?

hey guys, long time no talk lol. But I've been noticing after I finally got my rig up and running that my blower motor seems to be sucking up some monster voltage, when I'm running at highway speed about 1600 rpm (my best guess no tach) when the blower is on high my voltage will drop from 14.2 to 12.8 and at idle itll dip to 12.1 I'm just wondering if this is normal? It's an 81 cheyenne with the 5.7 diesel btw sorry I didn't mention that earlier

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Old 05-07-2012, 04:24 AM
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I had similar problems with my '75 GMC and it turned out to be a problem with alternator output. If I turned on the blower and lights at the same time I was only getting about 11.5 volts on the gauge. The fix was a new (rebuilt) alternator.

You may also have problems with your blower motor drawing too much power. However, the alternator should usually be able to keep up with it. GM uses a separate 30 amp line and fuse under the hood to power the high speed setting on the blower, so it is designed to suck down some significant amperage on high speed.

Bruce
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Old 05-07-2012, 07:35 AM
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Thnx bruce, I need to proof read better lol it was a late night and I just realized my title says buyer motor not blower motor. My alt is brand new though nothing touches my output other than that motor, I can turn the radio on hit my brights and flashers and wipers all at once and my gauge barely wiggles but I hit that motor and boom drop a volt and a half
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Old 05-08-2012, 04:52 AM
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Does this only happen with the blower on high speed? On a vehicle with AC the blower runs all the time on one of the lower speed, and when you push it up to high speed it kicks in the relay under the hood that is connected to the separate 30 amp circuit. If you only have trouble with high speed it might be related to the blower relay, but I doubt it.

The simple fix is probably to just replace the motor. They are easy to reach under the hood and not that expensive. Just bring the old one along to the store to make sure the new part matches.

There are some variations in the shaft length and fastener on the motor and you want to make sure you can reattach your old squirrel cage. I think the blower with the HD heat/AC package is different than the non-AC vehicles.

Bruce
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Old 05-08-2012, 08:32 AM
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I thought about that and yes its only on high when it does this but I just replaced the motor a month and a half ago because the old one had gotten water inside through the missing inspection plug and rusted solid lol I might just replace it anyway because like you said, they're cheap lol
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Old 05-08-2012, 08:35 PM
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resistor

Check out the motor speed resistor. It could be shorting to ground adding load when the motor is in high speed.
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Old 05-09-2012, 03:24 AM
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Coincidently I was pricing them today lol, I figured I'd try that before another new motor since mine is only a couple months old
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Old 05-09-2012, 07:51 PM
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If the blower resistors check out OK, I'd check the blower motor bearings. The extra drag will pull more current and load down the charging circuit. Can you reach the squirrel cage to check if it turns freely?

Ron
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Old 05-09-2012, 07:58 PM
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I can't reach it at all on the truck, but its three bolts and a connector and its off though
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