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Discussion Starter #1
Recently my blower fan started operating oddly. With the fan speed set at High the speed surges up & down.
While at idle it may slow down but speeds up to High again as you accelerate from a stop. All the speeds work so I don't think it is a blower fan resistor. The fan doesn't havr any obstructions that I can hear or see. Was working fine until just recently. My battery charge was low so I'm recharging the battery. Could a poorly charged battery cause this problem? If the alternator was bad or weak could this be the problem? When the fan is set at high and it is working properly it puts out strong amount of air. Where do I start looking?
Thanks
 

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Sounds like some resistance in the circuit. The fan will run at 12V for the high speed. Any slower speeds and the voltage is reduced though a dropping resistor. If any other resistance is in the circuit then you will get a further drop.
 

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Yes, low voltage will cause the fan to not spin as fast. SInce you said it varies on RPM, I'm going to lean on bad alternator or other charging system issues.
 

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Mine did that just slightly normally when I had my Taurus. The alternator doesn't make a full charge at idle. But it wasn't REALLY obvious unless you payed close attention to it. Now if it's a major change, then that is not normal. I also noticed that the headlights dimmed ever so slightly at night if you had to run the windshield wipers. But those do take some power so it's not surprising. That and the stock headlight harness is so woefully inadequate it's pitiful. It has a voltage loss STOCK across the wiring, so if you put a bigger bulb it it, it guarantees you burn out the socket on the headlight harness. Ask me how I know. :banghead:
 

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When this happens do you have any other heavy electrical draws turned on also? Like headlights, rear defogger, etc. As MrBooMY said, at idle your alternator cannot fully meet the charging needs until the engine is runs faster then an idle. If you have a lot of accessories running all at one, then this is pretty normal.


Was working fine until just recently. My battery charge was low so I'm recharging the battery. Could a poorly charged battery cause this problem?[/b]
Oh and yes this can have an effect. A weak or dead battery is a heavy load on an alternator. Get that battery fully charged. To fully charge a battery you're looking at about 10 hours or so. That's if it was completely dead.
 

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This started happening when i installed my UDP. As far as i can tell, its just a charging issue.


No biggie.
 

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If you have a UDP it's normal. Cause I have one on my 2002 VW Jetta VR6 and it does it every time it goes back to idle. It's a normal thing for me. UDP slows down the alternator so it doesn't charge as well. I have a stock crank pulley I got when my engine got hydro locked and while it was on I didn't have any charging issues even at idle. But I missed the extra power that it was sapping.
 

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Discussion Starter #8
What is a UDP? New update. Installed a new starter as mine had been acting up. Went to a shop that rebuilds alternators and he checked mine and said mine was ok. However there was excessive resistance between the battery and alternator. He recommended I clean all cable contacts at the battery,solenoid, and alternator post first. I did this but haven't yet rechecked the resistance he spoke of. The car had had a slight idle speed surge but this appears to have stopped and the fan is better somewhat but not yet normal. He said if the resistance was corrected to normal then and the problem still there then fix the alt. I see no dimming of the lights when using wipers, rear defroster,et. Surge of the fan speed in more pronounced at idle then driving but still there.
 
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