voltage drop air conditioner on

[chamilun]

I've been fighting a dead/dying battery for a while. Found no parasitic drains.

So attached voltmeter to car and drove around.

Battery without car running = 12.7

running = between 13 and 13.5

with air conditioner on, goes down to 12.3 or less.

Does this mean my alternator is defective, or is there a short somewhere?

don't know where to start, any help much appreciated.

thanks!

[86 911 Targa]

Keep in mind that while using the A/C, the current load on the alternator is quite high due to the condenser/interior fan.

It is not unusual for your system voltage to drop a bit under these conditions.

You may incur additional voltage drop(s) by adding additional loads to the system such as headlights ect..

Good luck,

Gerry

[chamilun]

Well, it appears that if voltage drops considerably with "electrical components" all turned on, you have a bad alternator. I guess the ac kicking on simulates this scenario.

I want to make sure before I replace the alternator that a short is not a possibilty. The low (<13.5) output tells me it has a bad diode(s)

[86 911 Targa]

Originally Posted by chamilun

Well, it appears that if voltage drops considerably with "electrical components" all turned on, you have a bad alternator. I guess the ac kicking on simulates this scenario.

I want to make sure before I replace the alternator that a short is not a possibilty. The low (<13.5) output tells me it has a bad diode(s)

Typically, if the VR diodes fail, the voltage goes high, and the battery get's cooked.

A lower voltage is most likely is the alternator.

Bentley's has a good chapter on this subject.

Have you tested the battery's specific gravity?.

Load test?.

V-Belt?.

Also, if possible, can you record the battery voltage, disconnect the battery overnight and re-measure the voltage in the am?.

The are several troubleshooting step you can take before "surgery".

Our alternator was completely rebuilt about 5K miles ago.

R&R(ing) the alternator was about a two hour job.

I'll take measurements tomorrow (static, running, running W/ A/C and lights,

and pm you.

Cheers,

Gerry

[chamilun]

Thanks Gary

The battery is new.

V-Belt has good tension.

If I were to drive the car for a while without the ac, and the battery stays charged,
would that indicate the alternator is just not able to keep up, or is there a short of some type in the ac wiring?

[86 911 Targa]

Originally Posted by chamilun

Thanks Gary

The battery is new.

V-Belt has good tension.

If I were to drive the car for a while without the ac, and the battery stays charged,
would that indicate the alternator is just not able to keep up, or is there a short of some type in the ac wiring?

Do a static current draw test. (see jpeg).

Go to a shop and get a load test on your alternator.

The battery's only function is to start the car.

Replacing that current drain and running the accessories is done by the alternator.

Once you have started the car, you could (if there was some way of preserving the diodes by some type of load), drive on the alternator.

However without a load, the voltage would ramp up on the diodes, and smoke them all.

Good luck,

GERRY

[86 911 Targa]

Here's the jpeg

[chamilun]

With anyone fighting these same symptoms, turned out was the voltage regulator. In retrospect, the key may be that if your voltage is all over the place (13, then 13.5, then 12.5, then 12, etc), its your regulator struggling to maintain steady output.

[smallac]

The other points: The battery's only function is to start the car and replacing that current drain and running the accessories is done by the alternator.