A/C blower motor causing charging problems

[krisj]

This is my first post since I introduced myself a few months back. I've been researching this issue but have not found a solution.
My a/c works great but since last week the fan motor causes a charging problem. When I increase the speed of the fan, the battery voltage gauge instantly goes down with each press of the fan speed switch. Anyone else experience this?

 

[df2x4]

That's a weird one. I'm sure someone will know more about this than I do but it sounds like the motor itself or the resistor one is drawing way too much amperage. Not sure how this could be the case as I'm sure the motor is fused somewhere. I had a blower motor burn out in my C1500 one day but I never noticed any voltage drop. Honestly the only time I can think of that I have seen major voltage drop that wasn't stereo related in my trucks was related to an intermittent alternator failure. Does the blower motor still function normally other than the voltage drop? Still move enough air, not making any weird noises, etc?

 

[krisj]

Except for the voltage drop (which does lead to dim lights and poor ignition rather quickly), there are no strange noises that I can detect and seems to otherwise function normally. Once I turn the blower motor off the voltage gauge goes back to normal (needle sits just a hair below the 14 mark.)

Also, I replaced the battery last month and my terminals are in prime condition.

 

[1997chevydriver]

Except for the voltage drop (which does lead to dim lights and poor ignition rather quickly), there are no strange noises that I can detect and seems to otherwise function normally. Once I turn the blower motor off the voltage gauge goes back to normal (needle sits just a hair below the 14 mark.)

Also, I replaced the battery last month and my terminals are in prime condition.

Take a DMM and test voltage at the battery at each level of speed.

 

[BackInBlack]

This is my first post since I introduced myself a few months back. I've been researching this issue but have not found a solution.
My a/c works great but since last week the fan motor causes a charging problem. When I increase the speed of the fan, the battery voltage gauge instantly goes down with each press of the fan speed switch. Anyone else experience this?

My gauge would dip way below the 14 mark(close to the red) with ac on high. I did the big 3 with 2 gauge wire and it was a huge improvement. I read somewhere about it maybe being the resistor making the gauge dip, i havent fixed mine just helped it out. Does your battery gauge bounce with the blinkers/hazards?

 

[krisj]

Yes, battery gauge definately bounces when the turn signals flash, but it was doing that before the charging problem started.

Sent from my SPH-M820-BST using Tapatalk 2

 

[krisj]

I'll get those voltage readings and report back later today. Gotta get a 9v battery for my dmm.

Sent from my SPH-M820-BST using Tapatalk 2

 

[krisj]

Take a DMM and test voltage at the battery at each level of speed.

I finally had some time to spend on my truck today. I tested the voltage at the battery and was 13.85 with A/C off. I checked the battery voltage at each level fan speed and the voltage at battery never went below 13.73. I'm scratching my head wondering why the gauge in the truck falls with each fan speed level.

 

[krisj]

Take a DMM and test voltage at the battery at each level of speed.

I finally had some time to spend on my truck today. I tested the voltage at the battery and was 13.85 with A/C off. I checked the battery voltage at each level fan speed and the voltage at battery never went below 13.73. I'm scratching my head wondering why the gauge in the truck falls with each fan speed level.

 

[96Z71ECSB]

I'm not sure why the gauge acts that way either. Testing the battery is a sure fire way of knowing if there is a voltage drop.
Test again with the A/C on and the fan on high. Also turn your headlights on high beam. Test voltage at the battery at warm idle. Then test voltage at the battery with engine at 1500 to 2000 rpm.
With the engine at warm idle, the voltage should be anywhere from 12.5V to 13.5V. With the engine at 1500 rpm, the voltage should be 13.5V to 14.5V. Sometimes almost 15V.
If the voltage at warm idle is lower than 12V, then you are probably looking at a dying alternator.
If the voltages check out, then I wouldn't pay attention to the gauge unless it drops below 12V.
If the gauge does drop below 12V, then retest voltages.

I'm not sure what year your truck is, but I did the AD244 upgrade to my '96 and it stopped all voltage drops/dimming of the headlights at idle.