Engine stalls when costing in neutral with A/C on.
 

I just finished installing the Classic Auto Air A/C kit into my '76 911S, all went well and the car finally has a cold cabin and pleasant to drive around in the summer, except for this annoying issue!, with the A/C, as soon as I reach a stop and depress the clutch, the RPM will drop severely, and most of the times the engine would stall, and that only happens when I have the A/C on, it would act normal when its off. I checked the AFR at idle and it was very lean at around 15, so I richen it up down to about 13, which made the idle much smoother, but still did not solve the issue, could it be the ignition timing?, do I need to set the idle more than 1000 rpm to compensate for the idle drop when A/C is on?

I think there is a device that alters the engine speed when the ac is activated. Not sure on a porsche but older us cars had a solenoid that pushed on the accelerator when ac was turned on

The extra load on the engine when the AC is on probably is dropping your idle. Not a bad idea to raise it a bit.

I raise my idle by a few hundred over the summer, then back down for winter. You'll never get the idle to sit at 1000 with the A/C on if you have it sitting at 1000 with the A/C off.

Modern cars have a secondary idle valve which opens when the A/C is in, acts like turning that idle control screw a turn.

kamaro...if your engine is dying going to idle with the A/C you are running too rich .Adjust your fuel mixture............

Ivan

Mine would die with the engine cool and the AC on. Leaned out my fuel mixture a fraction and everything normal again. Like Ivan said.

+1 and or a vacuum leak

With our Kuehl 507 compressor and a 3 condenser system in a 1973, 911T with webbers, I could idle the engine down to almost 500 rpms with the AC on, compressor clutch engage.

The a bit lean AFR is not too bad, after you chase the vacuum leaks, insure you have enough ignition advance, check the the low and high side pressure at idle along with the ambient temperature around the vehicle at the time. Excessive high side pressures do put a load on the crank pulley.