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1993 Suburban low voltage reading

Tiny
CLIFF FARRAR
  • MEMBER
  • 1993 CHEVROLET SUBURBAN
  • 315,000 MILES
I have a 1993 Chevy Suburban 4WD with dual A/C. It shows low voltage on the gauge most of the time, but particularly when idling at red lights or heavy traffic and particularly when it is hot outside. A/C makes the problem worse, but does not appear to be the root problem. I have replaced the battery and alternator with no improvement. Truck has never failed to start. This condition has been going on for several years.
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Sunday, July 15th, 2012 AT 9:45 PM

8 Replies

Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
Do you have a multimeter to do some testing?
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Sunday, July 15th, 2012 AT 9:50 PM
Tiny
CLIFF FARRAR
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  • 6 POSTS
Yes, I do.
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Monday, July 16th, 2012 AT 12:13 AM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
At idle what is voltage reading at the battery using you multimeter?Also with the ac on what does your multimeter read?
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Monday, July 16th, 2012 AT 3:16 AM
Tiny
CLIFF FARRAR
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  • 6 POSTS
The voltages at the battery are 12.31 with both air conditioners on hi and 13.49 with both air conditioners turned off. This is with the engine at idle with the truck in gear.
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Monday, July 16th, 2012 AT 4:30 PM
Tiny
SATURNTECH9
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How about with just the front ac on high?Looks like a nad alternator how did they test it?
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Monday, July 16th, 2012 AT 6:37 PM
Tiny
CLIFF FARRAR
  • MEMBER
  • 6 POSTS
This morning after the ambient temp rose to 85, the readings at the battery with the truck idling in gear were 13.69v with the A/C system off; 13.36v with the front unit only on hi. I also checked the voltage at the cigarette lighter and found the voltages lower; 13.20v with the A/C off and 12.32v with it on. The voltage will probably be lower this afternoon because the ambient temp is supposed to be near 100.

The alternator and battery have both been replaced since this started with no improvement. Old alt was tested at Advance Auto on their machine and tested good, but was replace anyway because the alt was cool when tested.
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Tuesday, July 17th, 2012 AT 2:50 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
Are you sure you put the correct alternator in when you replaced it?I mean the correct one amp output wise?
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Tuesday, July 17th, 2012 AT 8:35 PM
Tiny
CLIFF FARRAR
  • MEMBER
  • 6 POSTS
It was a 105 amp alternator which is what came on the truck as original equipment. There is a 130 amp alternator available, but it would require changing mounts and a different serpentine belt.
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Wednesday, July 18th, 2012 AT 2:10 AM

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