Ut oh, is my alternator dying?
07-22-2001, 12:36 AM
#1
Drifting
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The voltmeter drops close to 12V WITH the A/C running at idle. While driving all is fine. Without the a/c on, all is fine.
When the a/c is on and I'm stopped, to keep the volts above 12, I have to put it in neutral and rev the engine.... is my alternator dying or is this anothe problem? TIA
When the a/c is on and I'm stopped, to keep the volts above 12, I have to put it in neutral and rev the engine.... is my alternator dying or is this anothe problem? TIA
07-22-2001, 12:58 AM
#2
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When the a/c is on, the main fan is on which draws 14 amps, and the a/c compressor clutch is on (haven't measured its current). Along with any other electrical loads, your alternator cannot deliver full output at the slow idle speed, but can at higher speeds like when you get underway. Unless you sit idle for long periods of time, your battery will deliver the current your alternator cannot and it will be replaced when you begin moving in traffic. You might check to see if you have normal idling rpm and if you do, your voltage dropping to 12+ volts is normal and I wouldn't worry about it.
07-22-2001, 10:41 AM
#3
Racer
Originally Posted by jfb
When the a/c is on, the main fan is on which draws 14 amps, and the a/c compressor clutch is on (haven't measured its current). Along with any other electrical loads, your alternator cannot deliver full output at the slow idle speed, but can at higher speeds like when you get underway. Unless you sit idle for long periods of time, your battery will deliver the current your alternator cannot and it will be replaced when you begin moving in traffic. You might check to see if you have normal idling rpm and if you do, your voltage dropping to 12+ volts is normal and I wouldn't worry about it.[/color]
Mine does the same thing - it will get as low as 12.4 under similar conditions.
Last year my alternator went out - the symptom was 11.2 volts at idle and it never got above 12.5 at high rpm's.
07-22-2001, 07:52 PM
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What they said. Suddenly one day, 95 degrees out, in rush hour traffic idling, AC on full, watching the temp gauge creep up to 215, then suddenly it drops to 10.4 with a red bar next to it. Now it says battery, not coolant temp - then it dawns on me, 12 miles to go and I'm royally screwed. Starts to idle really rough. Turned all electrical off, got out of traffic & up to highway speed and once the fan turned off, I was getting high 11's indicated. Made it home on battery "vapors". Man that fan sucks a lot of juice!
07-22-2001, 10:43 PM
#5
Race Director
i have the same problem....replaced alternator 3 times same results, kinda makes me think its normal too! 
but that optima battery is keepin me goin'!
HEY HENDEJ.....high 11's on juice is NO good, it should be in the high 13's to low 14's, check that alternator out
but that optima battery is keepin me goin'!HEY HENDEJ.....high 11's on juice is NO good, it should be in the high 13's to low 14's, check that alternator out
07-23-2001, 12:36 AM
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Just a thought. I put two alternators in and then realized it was my dash gauge after I put a meter on the battery. So double check the alternator output with a multitester to see if it matches the gauge in the car.
07-23-2001, 06:19 AM
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I have the same problem. My 89Coupe Idles at about 12.3 or 12.4Volts. My Digital Dash Volt Gauge is off by a .5 Volts. It shows 11.8 on my dash. When I check the voltage across the battery, it shows up with 12.4volts.
-Tim
-Tim