does AC affect battery life?

[tonycarguy]

I've heard this before, that using the A/C more often will shorten the battery's lifespan. Why is that? The only 2 reasons I can think of are (1) the AC tends to raise underhood temps, and (2) using the AC requires the electrical fan to run more often especially when you're at a stop, thus potentially exceeding the charging system's ability to maintain the battery.

I don't believe #2 is a problem on modern cars because modern alternators are smart enough to maintain the battery. As for #1, this does seem to be a legitimate problem but not for cars whose batteries are located away from the engine like some performance cars.

Myth or real?

 

[javacontour]

I'm thinking the compressor clutch pulls a large amount of current in addition to the fan running.

At idle, I doubt the alternator is keeping up with the load with both the inside and underhood fans running as well as the clutch energized.

 

[JimFitzpatrick]

In my neck of the woods we use our A/C no more than six months a year (if that).I've always gotten at least 4-5 years out of my batteries but that certainly doesn't mean I couldn't have gotten more by not using the A/C.I think 4+ years from a battery is reasonable.

 

[Quattro Pete]

Originally Posted By: tonycarguy

Myth or real?

I'd say myth. But even if it does affect it a little, what are you gonna do? Stop using AC?

 

[otis24]

I was told by a GM rep at the dealership where I work that the battery never really gets fully charged when AC and various accessories are running. You can extend the life of the battery by putting it on a charger once per year. His father did this on the battery in his Hummer and the battery lasted ten years. I know that we drive our van very short distances at times. I am on the third battery in my 2005 Grand Caravan. Factory battery lasted about 18 months. Same for the Napa Gold that I replaced it with. I currently have a Napa Gold. Will put on a charger once per year from here on out.

 

[440Magnum]

I don't believe it. Any alternator worth its salt can run all the AC systems just fine at idle these days. In fact when I retrofitted my '66 Dodge with a big-honking electric fan in place of the engine-driven fan, I took plenty of voltage measurements with the AC on, cabin blower on high, and the radiator fan at maximum speed, idling in gear just to be sure I wouldn't have that exact problem on an older car. The voltage never dropped below normal until I added the high-beams and windshield wipers (essentially every electrical load the car has, short of the stereo and my iPhone charger). And then it was only a few tenths of a volt low, and came up to normal again as soon as the engine went above ~1000 rpm. I'm running a 1990 vintage Denso alternator off a Dodge pickup, 130 amp model.

 

[duaneb9729]

another myth

 

[brianl703]

Originally Posted By: javacontour
I'm thinking the compressor clutch pulls a large amount of current in addition to the fan running.


The compressor clutch can't pull that much current. The wires are skinny. The terminals in the connector are tiny. A google search suggests 4 amps for a Mopar C171 compressor. I would have guessed 5.

 

[oldmaninsc]

Originally Posted By: duaneb9729
another myth

I agree

 

[CROWNVIC4LIFE]

Originally Posted By: oldmaninsc
Originally Posted By: duaneb9729
another myth

I agree


X3

Even it was not a myth and it did shorten the battery life I doubt many people in Miami-Dade County would shut the a/c off..Everyone I know just leaves the a/c on all the time all year long..Ours have been on since the day we got our cars..I am happy to get 4 years out of a battery down here in the jungle.

 

[HTSS_TR]

It may not a myth, remember that batteries in warmer climate didn't last as long as in cooler area, may be because the use of A/C more often.

 

[eljefino]

It might relate to "harder cranking" if you leave the AC on when you start the car... if you have something non computerized from 1975.

Anything made in the last 15+ years has the AC clutch controlled by the computer, and it engages a few seconds after the engine catches. This lets the PCM do tricks like kill AC when overheating or at WOT.

 

[mechanicx]

Well heat kills car batteries. Maybe higher temperatures and using A/C got associated with batteries dying when the heat would've got them anyway. I know when I lived in TX car batteries would conk out a lot and adding water would get them working. I think for a hot climate a non sealed battery you can add water to is useful.

 

[wrcsixeight]

Well every vehicle is different, but if I have my blower motor on High, and my headlights on, with my engine at full temperature, 10 amps are flowing from my batteries at idle speed. The alternator cannot keep up.

The hotter the alternator, the worse the low rpm amperage is.

AC makes the underhood temps higher.

I certainly think it is plausible that the AC causes the battery to deplete if idling is excessive on max A/C in combination with other battery abuse.

 

[javacontour]

Originally Posted By: brianl703
Originally Posted By: javacontour
I'm thinking the compressor clutch pulls a large amount of current in addition to the fan running.


The compressor clutch can't pull that much current. The wires are skinny. The terminals in the connector are tiny. A google search suggests 4 amps for a Mopar C171 compressor. I would have guessed 5.


If I had given it a bit more thought I would have figured that out. What type of load is this? Is it a continuous load, or a surge current that eventually drops like an electric motor?

 

[SteveSRT8]

This thread is filled with misinformation.

This issue is extremely platform dependent. For example, in most GM products the ac on max will actually cause the idle to be raised just enough to correctly charge everything.

The Fan in overdrive can draw like 35 amps!!!

And in my chrysler the fans run continuously on very low speed anytime the ac is on, even with compressor disengaged. This makes underhood temps much lower than with AC off!

 

[brianl703]

Originally Posted By: javacontour

If I had given it a bit more thought I would have figured that out. What type of load is this? Is it a continuous load, or a surge current that eventually drops like an electric motor?


The clutch is an electromagnet. I wouldn't expect it to have much of a current surge when turned on. The 4 amp reading is continuous, you probably couldn't see the surge current without a scope.

 

[brianl703]

Originally Posted By: SteveSRT8

This issue is extremely platform dependent. For example, in most GM products the ac on max will actually cause the idle to be raised just enough to correctly charge everything.


My Saab 93 monitors the duty cycle of the field coil, and if it remains high, it increases the idle after a few minutes. It works whether the load is the cooling fan or a 1000W inverter..

 

[440Magnum]

Originally Posted By: eljefino
It might relate to "harder cranking" if you leave the AC on when you start the car... if you have something non computerized from 1975.


My 1960s Mopars kill all the electrical accessories whenever the engine is cranking. Its a dirt-simple extra terminal in the ignition switch- accessory power is separate from ignition power and the accessory terminal is de-energized when you turn the key all the way to "crank," it comes back on when the key snaps back to the "run" position. My old Fords were that way, too. In fact, I've never owned a car that you *could* crank with the AC clutch engaged without hot-wiring it.

 

[rslifkin]

It varies based on the vehicle. In my Jeep, the ignition switch is set up the same as 440Magnum describes, with accessories cut during cranking.

As far as underhood temps, being that the e-fan runs whenever the A/C pressure gets too high (basically, if the A/C is on and you're not moving fast enough), it helps keep the engine bay cooler than the same weather without A/C.

The alternator can keep up just fine at idle with the A/C on. With the fan on as well, the voltmeter drops just a hair at times (from say, 13.8 to 13.6 - 13.7). Above idle, every accessory, e-fan on high, etc, won't dip the voltage. I'd say the battery stays charged just fine.