Lower voltage at idle - AC Blower, Alternator, AC Compressor, or other??

[tres0422]

Problem: Voltage needle sits around the centermark on the dash voltage needle....9V?

History:

- Truck wouldn't start 3 weeks ago. Zero voltage after sitting at work about 10-11hrs
- Replaced battery and it started.
- I felt the volatage was a little low so I replaced the brushes on the alternator and tightened the belts
- I noticed it has been hard to start 2 times over the past week.
- I noticed the voltage needle rides low, just above the centermark on the voltage needle, while at about 600-700rpm in "D" with AC on and fan on high.
- While above 1000rpm in "D" with AC on and fan on high the voltage needle rides where I expect it to, asignificantly above the centermark...Around what I assume is 12.5-14v.

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What I see:

1) When at 600-700rm idle in "D" with AC ON and FAN HIGH the voltage needle is right above the centermark 9-10V
2) When at 600-700rm idle in "D" with AC ON and FAN LOW the voltage needle is about 12-14V
3) When at 600-700rm idle in "D" with AC OFF and FAN high the voltage needle is right above the centermark 9-10V
4) When at 600-700rm idle in "D" with AC OFF and FAN LOW the voltage needle is about 12-14V

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What I think:

1) The AC compressor isn't an issue
2) The alternator is old but doesn't seem to be a problem yet.
3) The blower fan is getting old and for some reason being a current sucker

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You guys have any ideas on upgrades, remedies, or things I haven't thought of to solve this problem?

Thanks,
Tres

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[Tools R Us]

Beg, barrow, steal a volt meter, what does it actually read?

 

[tres0422]

So how is the best way to read the DMM....I have one...

I guess just hook it up to read from the ash tray?

What should I expect at 600-700 rpm in drive? What is considered low?
Thanks,
Tres

 

[SiRaDuDe]

My '94 idles warm at 900rpm when AC is on... (in park)

If that helps out in any form...

Read battery terminals with engine stopped.... Just to get a battery base line, (around 12v)
Then read battery terminals with engine running (idle in park & AC OFF) you should be at 14v
Remove battery terminals (engine should still be running) read voltage at terminal cable ends (this should give you the ALTs actual charge voltage) should be 14v

If this checks out your Alt is fine.

P.S.
Never trust a stock Gage..

 

[tres0422]

Ok....so there is a resolution....THE FREAKING BELTS!

On my way home the voltage needle was reading low.....no matter what I did with the AC.....so I replaced the belts and 40 min later life is good. 13.2v with the car off. 14.5v with AC on and the car idling.

Thanks for your help.