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'97 Chevy Astro, 123,000 miles, 6 cyl, 2wd, auto, low volts

Merry Christmas guys. Christmas eve I went to mail a letter and the window wouldn’t go back up. I then noticed that the voltage gage showed about 13 volys instead of the normal 14. As I drove away the voltage went back up to 14 and I could close the window. Idleing at lights the voltage dropped back down. The barrery is 1 year old, terminals clean, and has water. The alternator was rebuilt at about 80,000 miles. I figure the alternator brushes are worn and need to be replaced again. Wanted your opinion before heading to shop on Friday.

When a load is applied (no matter what the load is) the voltage will drop because the load (amperage) increases. That’s normal but should not be that noticeable under a comparatively light load such as a window motor; unless the motor or window regulator is dragging or binding.

Maybe you have a glazed belt running the alternator and it’s slipping a bit even though it may not appear to be so by watching it. Another possibility is a binding or weak belt tensioner.
With the engine off, a socket/ratchet could be put onto the alternator pulley nut and one could attempt to rotate the alternator. You should not be able to do without a great deal of force. If it does spin then the belt or tensioner is at fault.

The tensioner was replaced within the last 2 years but I will look at that first. The window was just one symptom. The voltage dropping every time I stopped was the most important. A loose belt could answer that too.

Recently I had an alternator fail on my car and replaced it with a reman unit from O’Reillys.
Upon startup the alternator would not charge at all and every test showed the alternator and the wiring, fusible links, etc in the car was also good.

A visual inspection showed nothing wrong with the alternator pulley but the belt would simply not get a bite on the pulley. I could rotate the alt. pulley with a socket while only using a moderate amount of force.

The guy at O’Reillys tried to argue the point with me that there was nothing wrong with the pulley but finally caved and ordered another alternator. Installed that, the pulley would lock down solid with the belt. and the problem was solved.

How long had it been since the car had a mid to long drive? I am thinking maybe the battery was just a little low and it had been close to the break off point for the voltage display and nothing is really wrong. You might want to check the voltage with a good digital meter to see where it really is (engine off and engine on). You also may stop by your local auto parts store and have them give you a battery and alternator test. Most will do it for free and most do a fair job at it.

I mainly just drive the van to work and around town, maybe 30 miles then return home. It had sat for a couple of days but no more. Drove it today and everything was fine. Hopefully it is not on the verge of something going out. The regulator part of the alternator was my best guess after checking the belt. The voltage on the battery is 12 volts without the engine on.

A good, properly charged battery should show about 12.6 volts on a voltmeter. If it’s showing 12 volts even or near 12 then either the battery is failing, not being properly charged, or is slightly run down from sitting.

Can YOU read the voltage with a multimeter with the engine running? With the engine running, the voltage should be 13 1/2 to 14 1/2 with engine rpm above 1,000rpm and accessories (electric motors) OFF.

I meant to say 12v with the engine off. With the engine on it is 14.1v

What were getting at is a battery puts out 2.1 volts per cell,so your standing voltage should not be lower that 12.6 volts, if it is you are dealing with a battery that is partially discharged from the start.

Drove several times today. 14.1v driving and drops to about 12.5 when idling. If I rev the engine the voltage goes up. The shops open again tomorrow so I can get the alternator and battery tested. Battery is one year old and the terminals are clean. My volt meter is 30 years old but close enough for my work.

It sounds to me that the battery is getting weak. A load test of the system will show up what the problem is.

12 volts should be adequate to raise and lower a window. The window motor, wiring, mechanism are suspects as causing too much drag/load.
Place an ammeter (NOT your multimeter) between the battery post and battery cable terminal. Run the right window up, and note the amperage. Run the other window up, and note the amperage. How do the amperage draws compare?

To me that sounds like the charging system. Have you had it checked as I suggested yet? We can only guess, but if you bring it somewhere where they can load test the battery and check the charging system, I suspect you will find the answer without relying our our guessing.