Alternator charging

[dixiechevy01]

I have an 87 k5 blazer with a 350tbi, I was driving home in the snow the other night had it in 4 hi, headlights on, wipers on, and the defrost on high and it seemed like the alternator surged and the belts squealed and the voltmeter went down around 12 or 11 volts. So I turned the defrost off and it was ok after that. It did this a few times after that also but it seems like its only if I have it on defrost with everything running.

I was thinking loose belts or the alternator might be bad. It was replaced about 3 years ago and I don't put that many miles on this. The belts were ok the a/c belt could be a little tighter but I didn't think that would affect the alternator because its on another belt. I was also thinking the gauge of wire from the alternator to the battery might not be thick enough. What gauge should be run for that wire and if anyone has any other ideas let me know.

 

[4xcrazy]

Shouldn't have been the belt, you should have a serpentine style belt on that thing running the alternator, not full serpentine, but a flat multi-ribbed belt.

Possibly the blower motor screaming because it's going bad and starts wobbling in the cage housing. I had a few do that. Annoying.

The blower motor starts screeching like that, essentially vibrating or wobbling and draws a bit more power, loading up, like trying to stop it by hand would.

 

[diesel4me]

I agree it sounds like a short circuit put a heavy load on the altenator,and seeing it stopped with the heater blower off,thats what I would suspect being the source of excess load..the blower motor on more than one of my old trucks make a severely annoying "SCREEEEEECHHH" when its below 10 degrees out,shortly after you turned it on...

Sounds like a main bearing just spun and is wiping the block out!--scares the crap out of you till you realize what it really is making the noise!..usually only does it a short time,on lower speeds,then it gradually goes away...I drill a tiny hole in the motor's bearing "bump" on the firewall side and put a few drops of light oil in it,that cures it for another few weeks usually..

 

[byggyns]

First, tighten the AC belt. In defrost mode, the system cycles the compressor to remove moisture from the air in the cabin, which helps to remove fog from the windshield. That is probably what is squealing.

Next, the voltage / alternator issue is probably elsewhere in the system. I think the blower circuit is the place to start looking for that one. But, with a 25 year old truck, the charging wire might be bad. Time and electricity are not kind to metal. My understanding is that you need at least a 10 gauge wire for a factory alternator. You may want to go up even to a 8 or 6. 4 or larger is probably overkill.

 

[4xcrazy]

Forgot about the AC compressor deal, if it's even hooked up and is working, that will also draw a decent amount of power from the charging system, you will notice a drop in gauge level when that thing kicks in, especially if everything else is going full on.

 

[dixiechevy01]

The blower motor was replaced a few years ago. But the blower motor speed switch doesn't work on one of the speeds maybe the switch itself is shorted out.

The squealing definitely sounded like a belt so I need to tighten the belt anyway. Yea the alternator belt is a flat 5 rib belt.

The alternator charging wire isn't that old I don't remember exactly when I replaced it but it wasn't that long ago maybe less then a year ago. Its probably a 10 gauge wire. Would it hurt to use a bigger gauge for that wire? And what amp alternator should I have?

 

[rampage]

Its probably a 10 gauge wire. Would it hurt to use a bigger gauge for that wire?

It never hurts to use a larger gauge wire -gives more current capability and less resistance. It only hurts when you use a smaller gauge.