A/C drops voltage... why? - JeepForum.com
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post #1 of 8 Old 08-20-2008, 03:39 PM Thread Starter
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1994 XJ Cherokee 
Join Date: Aug 2008
Location: Wilmington, NC
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A/C drops voltage... why?

Hey, I have noticed that when I kick on my A/C, my voltage drops from 13.8 to 12.4... I was curious if this is normal or is something wrong. My A/C blows COLD air, just like new. I know my running voltages because I have a radar detector with voltage meter built in as well as my dash has the voltage meter on it. There is a power lost too. It's not a big power lost, but it's noticable. What could cause this. Thank you in advance.


PS - I did try searching the forum here but couldn't seem to find anything. Maybe a point in the right direction.

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post #2 of 8 Old 08-20-2008, 04:14 PM
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1992 XJ Cherokee 
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Location: Sioux Falls
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Maybe the electric radiator fan is drawing too much juice? With the engine off and cooled down, spin the electric fan by hand. It should spin with a little drag. Is it's really difficult to turn then there's the problem maybe.

Just my .02
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post #3 of 8 Old 08-20-2008, 04:21 PM
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1997 XJ Cherokee 
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Normal. Not only does the compressor slow the engine down (thus slowing the alternator) but it also kicks the aux fan on which draws a fair amount of amps itself.

**1997 Jeep Cherokee SE**
Former Police Car assigned to 54-26, RIP.
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post #4 of 8 Old 08-20-2008, 04:30 PM Thread Starter
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1994 XJ Cherokee 
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Ehh. My fan turns perfectly fine. I am just not use to having the A/C on the Jeep, not working anyways. That and my other cars didn't show more than a -.2 voltage drop.
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post #5 of 8 Old 08-20-2008, 09:55 PM
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1990 XJ Cherokee 
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My jeep does the same thing, also when i turn the heater on
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post #6 of 8 Old 08-20-2008, 10:05 PM
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1995 XJ Cherokee 
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Mine too. The battery is probably seeing higher voltage than what the gauges read. The voltage drop will almost all be from the fans. The compressor will reduce the power available to the trans. but won't slow the alternator as the engine speed is controlled by your foot except at idle where the computer keeps it from dropping.
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post #7 of 8 Old 08-21-2008, 09:11 AM
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1996 XJ Cherokee 
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I think everyone's does this. The voltage reading is showing voltage after draw. So your battery should still be seeing 13.5 volts, even though your cigarrette lighter only shows 12.4.

The blower has a lot of draw as does the e-fan. If you switch it from a/c to vent, my voltage drop is usually just a little better, but that's because the a/c clutch doesn't kick in, and the e-fan doesn't turn on. But that blower is turning away, so I've always just blamed the blower motor. It's not bad, just power hungry.

1996 XJ Classic
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post #8 of 8 Old 08-25-2008, 09:30 PM Thread Starter
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1994 XJ Cherokee 
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Hey, found the problem. It's the blower. The A/C only drops it by .2 volts. Blower drops it from 13.4(+/-) to as low as 11.8 volts.
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