Do I need a new alternator?

[sigchuck]

Hi guys, I posted a couple months ago about a potential charging issue with my '83 911SC.

I was having a Carrera oil cooler installed, and the shop let me know car died after idling for about 25-30 minutes while they let it warm up to check for leaks.

Having never experienced an issue with the charging system (no dim charging light, etc.), I decided to get a top notch, $10 cigarette lighter voltage meter.

I've watched it over the past couple months and voltage consistently stayed in the 12-12.8 range, depending on whether I was moving or sitting in traffic idling. I assumed bad voltage regulator and have had a new alternator sitting on the shelf ready to be installed.

This morning, the temperature in DFW finally dropped into the 60s so I wasn't running the air conditioner. To my surprise, voltage was a consistent 13.8-13.9 on my 25 minute commute.

Obviously the AC puts some load on the system with the evaporator fan, the front condenser fan, and the fan that's on the wheel well condenser I added. I don't think the SC electrical system (with 75 amp alternator) was designed with factory AC in mind, but does it seem correct than an otherwise functioning alternator shouldn't be able to keep up?

I do have an inline fuse for the front blower motor which I know has a propensity to seize/meltdown, and I haven't experienced any blown fuses.

I also have a cracked fan housing which I was considering replacing with a new Carpoint housing. I think these are made to fit the Carrera 90 amp alternator, and I'd need to buy a spacer to use my SC alternator. I'm considering just going with a Carrera alternator and selling my new SC one (hopefully any loss on the sale won't be more than the cost I'm avoiding for the alternator spacer). Of course I'd prefer to avoid replacing the alternator if you guys think it's otherwise functioning fine and I'm just putting too big of a load on the electrical system with the AC running. On the other hand, I have no plans to stop using the AC when needed, so in that case, would my best bet be to use a Carrera alternator?

Thanks for the help!

[dhanl82]

Good morning,

Some thoughts - I have a 1982 SC that also has a cigarette lighter volt meter installed.

My alternator is almost new and my meter reads 13.8 - 13.9 without the a/c on, with it off about 13.2 - 13.5 depending on idle rpms.

I recently replaced my ignition switch because the "switched" power in my car was running about 1.0 volt less than direct power from battery - new switch corrected this with the result that the cigarette volt meter now reads accurate charging voltage.

I was also concerned about the load on fuse # 20 that has both a/c fans running through it. I removed one of the fan wires from # 20 and connected it to fuse # 19 which is for headlight washers - that I do not use - and is also 25 amps. This way, I have separate fuses for each fan motor - no heat at all at either fuse.

I also have replaced my transmission ground strap.

Bottom line - your car's alternator is producing similar to mine and I have no issues.

[stlrj]

" ...would my best bet be to use a Carrera alternator?"

The Carrera alternator has an internal voltage regulator, yours is external, if I recall.

[timmy2]

His ‘83 should be an internal VR.

[sigchuck]

dhanl82, thanks for letting me know your experience!

Yes, my VR is internal to the alternator. I think they all went internal in '80 or '81, but in any event, mine is internally regulated.