Is this normal?

[87ChevyR10]

Some how, I got the idea that alternators were supposed to pick up extra loads. Well, here's the deal, when the truck is sitting idle, the voltmeter needle will be just passed the 3 of 13 on the gauge. Now, the headlights don't make a dent; but when I turn on the A/C, the needle drops to the left of 13. Since I only have 1 fan speed (high), it'll drop the needle close to 8 volts. Turning the A/C off kicks the needle back to the right of 13 again.

If I drive with the A/C on, the needle will drop some, but not as bad as if I'm sitting idle.

Is this normal or should the alt. be picking up the extra load?

 

[HotRodPC]

Kinda sorta is normal. That compressor draws alot of voltage and then you have the fan going to. This is also sometimes why some vehicles use a high idle solenoid so that when the AC is on, the idle will pick up a bit. If it's not dropping you down below 10 volts I don't think I'd worry about it just yet.

 

[Boone83K10]

another solution is just turn off the AC...

 

[87ChevyR10]

another solution is just turn off the AC...

I don't run it much. Just enough for the pump to cycle and stay lubed.

 

[HotRodPC]

If I have AC, you can bet your ass I'm running that ****. I don't care what it costs in mpg or down to 10 volts while idling at a red light. For that few seconds at a red light, I have a foot. I can hold the idle to 800-1000 or so from 500-600 to keep the volts up.

 

[350runner]

X2 gotta have AC

 

[Stewzer55]

I say fix your fan speed controller and look into upgrading your alternator.

 

[highdesertrange]

do you have a high idle switch? if you don't you need one. all vehicles with ac's kick up the idle or cut back the ac one way or another. highdesertranger

 

[HotRodPC]

do you have a high idle switch? if you don't you need one. all vehicles with ac's kick up the idle or cut back the ac one way or another. highdesertranger

Yep, aka High Idle Solenoid. Which should be energized when the compressor comes on, and off when the compressor goes off.

 

[87ChevyR10]

do you have a high idle switch? if you don't you need one. all vehicles with ac's kick up the idle or cut back the ac one way or another. highdesertranger

Yeah, the idle kicks up a bit with the a/c on; but, it's not enough to compensate for the low voltage. For now, the a/c only gets cycled to keep it healthy; otherwise, the truck usually only gets driven when the weather isn't good enough for my motorcycle or for getting groceries.

 

[bucket]

Could be an inaccurate gauge too. I've seen them drop an indicated 3 or 4 volts when in reality the voltage only drops by a volt or so.