Correct alternator for add on A/C?
 

The car is a '69E with a '73T motor (MFI). I don't know specifically what alternator it has, but when I added the A/C unit the shop owner (knowledgeable guy, for sure) said my alternator was fine and I didn't need a bigger one. (which he could easily have sold me without any questions). Since the install in April, the car has had 2 episodes of not starting, requiring a jump. In both cases I'd run the AC that day.

I bought the car at RM auctions, so don't know the history of the batteries in the car. I asked a different tech to swap the 75amp alternator i have in my '74 Carrera (no AC) but he said it wouldn't fit.

Now maybe, the batteries are just toast and new ones are all i need, but if I need a bigger alternator, I wanna do it. If so, which one would I get that will fit?

thanx steve

Test the batteries at a shop first.

thanx so much, that's on my agenda, as well as an alternator test. thanx s

which reminds me...this my first experience with 2 12V batteries in parallel. when you test the alternator (in the car) which battery do you test, or both? and how 'bout looking for a parasitic current leak? thanx. s

Test both independently.
Do you suspect a parasitic draw?
Using just one battery connected, put an ammeter in series with the ground strap and the negative terminal of the connected battery to measure any current flow.
If more than just the clock, pull fuses one at a time to see which circuit it goes away on.

thanx Dennis, that's how i was taught, as well. s

The AC draw is not that great. If your batteries and alternator are OK, there has to be a draw from something else.

One of the many upgrades I did to my 911 is send the tachometer in and had a volt meter built right into the bottom of the tach. That way the voltage is right in my face and easy to monitor. It looks right, as if it was factory. Why Porsche did not put in a volt meter is beyond me.

So like the others said, check the batteries.