Volts drop when A/C is on - The 1947 - Present Chevrolet & GMC Truck Message Board Network

GalloNegro · 06-25-2009, 12:41 AM

Newbee here, I have a 1987 SWB when I turn on the A/C my volts drop big time could the reason be the altenator.

Prong · 06-25-2009, 05:17 AM

If it's at idle, that's to be expected. Does it rise with some more RPMs? If so, you should be ok.

babyJay · 06-25-2009, 06:39 AM

Some drop is to be expected at idle as Prong said. Are you measuring the volts with the stock guage or a voltmeter? The volts shouldn't go down a lot like down into the 10 or 9 or 8 range, definitely a problem if it goes that far. Welcome to the site too, by the way.

454HO · 06-25-2009, 08:35 AM

Quote:

Originally Posted by GalloNegro

Newbee here, I have a 1987 SWB when I turn on the A/C my volts drop big time could the reason be the altenator.

The short answer is yes, it could be the alternator. But it could be a lot of other things too. Need a lot more details before a definitive answer can be given.

swb85 · 06-25-2009, 09:17 AM

The a/c and hvac fan both pull a significant load on the electrical system. Like said above, unless volts are dropping below 12V then it's nothing to worry about. I've got a 100amp alternator on my truck and when the a/c is on max/high and the electric radiator fan is on, my voltmeter drops to 12.5V at idle (I normally see 14V at idle).

06-25-2009, 12:41 AM	#1
GalloNegro Registered User Join Date: Nov 2008 Location: Tempe, AZ Posts: 9	Volts drop when A/C is on Newbee here, I have a 1987 SWB when I turn on the A/C my volts drop big time could the reason be the altenator.

06-25-2009, 05:17 AM	#2
Prong Registered User Join Date: May 2007 Location: CO Posts: 474	Re: Volts drop when A/C is on If it's at idle, that's to be expected. Does it rise with some more RPMs? If so, you should be ok.

06-25-2009, 06:39 AM	#3
babyJay Arrived on a Pale Horse Join Date: Mar 2007 Location: SnagTown Indiana Posts: 2,524	Re: Volts drop when A/C is on Some drop is to be expected at idle as Prong said. Are you measuring the volts with the stock guage or a voltmeter? The volts shouldn't go down a lot like down into the 10 or 9 or 8 range, definitely a problem if it goes that far. Welcome to the site too, by the way. __________________ Jason 87 V30 350TBI/400 White w/Boss V-plow 89 R3500 CC SRW

06-25-2009, 09:17 AM	#5
swb85 On a budget like Fred Sanford Join Date: Oct 2005 Location: Topeka, KS Posts: 2,031	Re: Volts drop when A/C is on The a/c and hvac fan both pull a significant load on the electrical system. Like said above, unless volts are dropping below 12V then it's nothing to worry about. I've got a 100amp alternator on my truck and when the a/c is on max/high and the electric radiator fan is on, my voltmeter drops to 12.5V at idle (I normally see 14V at idle). __________________ '85 Silverado swb: 383 stroker, 10.5:1, vortec heads, 232/238 roller cam, RPM air gap, performer 750 carb, stainless longtubes, 3" duals/super 44's, T56/4.11 383ci build / exterior refresh thread '98 Camaro z28: 370ci twin turbo 370ci build '01 Tahoe LT 4x4: 5.3, longtubes/ory, magnaflow duals, custom tune....wife's DD



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