From my experience, when turn the aircond on, it starts to ping, black smoke appear from exhaust. There is also a significant voltage drop in charging system (looking at my voltmeter). So I serviced the alternator, change all bearings, clean all connectors, change the carbon brush and then reinstall the alternator.
Then no more pinging. Aircond runs smoother and quieter, no more voltage drop even when switch on two large spotlight. I've push the pedal to the floor and still no pinging. So, I assume my problem is due to alternator overload when aircond system switched on. I've explained the problem earlier in other thread
Just my experience. Dont blame me if your pinging problem still occurs