Hey all - search didn't really help me out with this at all so I figured I'd make a thread in hopes of getting some suggestions.

With it being winter, I've been running the defrost a lot... sometimes on full blast or the setting just below full blast to keep things clear.

Noticed that when I'm slowing down to stop or turn that the blower fan will get much quieter and blow less hard for a second or two and then return to the normal noise/output.

I just changed my alternator recently so I was worried that I was low on juice or something, but I actually upgraded the alternator (CS144) and have observed on the back of trucks / other cars that my headlights do *not* dim, and my voltmeter stays consistent at high 13's or low 14's even.

Thanks for any suggestions!

Does yours have the digital climate control, or just regular knobs and switches?

A motor pulls more current than a head light.
Did this happen after getting the "up-grade"?

I think when you hit the brakes, the light pulls more power and drain the voltage.
Check your battery voltage with AC on at 3rd or 4th speed, head lights on, rear defroster on and wipers on. If you still have 13V or above at IDLE, you should be good.
I stay with Denso because they are super reliable.

It would typically take more than a .5 volt change to hear a difference in the blower motor. I'd suspect a bad connection somewhere in the blower circuit rather than an issue with the alternator.

Sounds like a non oem alternator issue to me. LOL. I have had a bad alternator in the past cause the same issue.

Well that's unpleasant to hear Jay hah.

I didn't notice this last year, but I hadn't used defrost this season prior to doing the alternator upgrade. Also upgraded battery ground to chassis and alternator to battery at same time wire with 2 gauge 100% fine strand copper wire, none of the cladded stuff.

Prior to doing the upgrade I could make my battery drop in the high 11's on extended bass notes with sub woofer, afterwards I still maintain high 13's/14's no matter how loud I'm playing music (and with headlights, aux lights, etc). Oddly enough, the problem persists even if I turn the head unit and amp off. Also does it with all the lights off, rear defroster off, etc.

So as convenient as it'd be to pinpoint the alternator, I think it may have something to do with the blower or wiring to it based on the above. I have the manual knobs Jeremy.

Thanks guys. Not sure how to go about testing the wiring or blower motor itself but I'll keep goin'

Mine does the same thing but my interior lights dim also

Found a good stretch to test where I could look at voltmeter closely as I was slowing down. Even with the blower motor off (just headlights, stereo muted), when I'm going a couple miles per hour my voltage drops to low 13's or high 12's. It bounces back a second later, but this is definitely the culprit. Otherwise it's at like 14.2 while cruising. When idling (550-600 rpm) I'm also at 13.9-14.0v.

So, that's odd. It's almost like the alternator produces no juice when I'm arriving at a stop, even though my rpms are at like 700? rpm or so. And it definitely puts out power at 550-600 rpm. Baffling.

I have the exact same problem in my '98. Replaced the alternator recently which made it a bit better. Usually notice it driving I-70 with the heater on.

My DD has done the same thing for years. Doesn't even worry me.