[MarkS]

A year ago, during the heatwave, I (foolishly) put on the AC.
~10 minutes later, the engine stalled while idleing.
When the engine restarted, the alternator light came on.
Inspection showed the alternator belt was destroyed.
As I didn't know the last time it had been replaced, I had both alternator and AC belt replaced.
I haven't used the AC significantly since, until the heatwave a week or so ago.
So I put on the AC again.
After ~15 minutes, the engine stalled while idleing. When I tried to restart the engine, it turned over, but very slowly, like something was trying to stall the engine. After 3 attempts, it did restart, running rough and slow. After a few seconds, a significant amount of smoke came from under the bonnet. After ~20 seconds of smoke, it stopped, and the rough slow running went away.
The alternator belt was occasionally running off centre on the tensioner pulley.
My suspicion is that the crankshaft pulley is splitting along the rubber.
But something caused the engine to stall twice, and run rough once, and generate smoke.

Since then the problem has not reappeared, but I have not had the nerve to put the AC (ECON) on.

As background information, I recently replaced the brushes on the alternator with secondhand brushes, and I have a long-term slow leak from the PAS pump centre gasket, onto the alternator and AC compressor. I have obtained and will replace the gasket very soon.

Sometimes when the engine is warmed up, and I put the PAS on full lock, I have observed the alternator belt virtually come to a halt, together with the alternator light, like the belt is slipping on the crankshaft pulley, but only when engine has had a good chance to warm up. The PAS fluid level is below minimum, but above the dipstick tip.

Occasionally smoke has been seen to reissue from under the bonnet.

I suspect an AC pump seize, or an alternator seize, or a water pump seize, or a PAS pump seize, but which one?