Idle Voltage with AC on

I suspect something wrong with my alternator/electrical system: with AC on and radiator fan/inside blower motor on medium setting the voltage measured on the battery drops under 13V to 12.6V.

From your experience: is this consumption normal for this scenario?

Without AC on the idle voltage stays around 13.8V to 14V.

I would expect that if you had the blower on full blast, Rear defrost, lights and the like... There may be an issue with your charging system...

Low voltage at idle with high load is not really unusual, but if this is a discrepancy with what you are used to, yes you can question the fact. part of my diode pack was shot at some time but the impact was more severe than that. What is your idle RPM? 600? Anyway, I'd expect the alternator able to keep the volatge with the conditions you describe. If you do not have any problems other than that....and voltage goes up as soon you rev the engine, I would not panic....but
Both my diode pack and then the voltage regulator were shot on mine...the original GM parts are POS....replaced the diodepack with BOSCH ....then 1 or 2 years later, the regulator. If you can handle a soldering gun, change the components, save the alternator.

This is the third alternator after the original and a remanufactured one.

The remanufactured alternator kept a voltage of 14.7 on idle but died after 3 weeks and a few hours of running the AC at full blast.

I've heard that alternators don't like high temperatures or a sustained high-load and that was exactly what it got before it failed - these days we have more than 120'F at ground level here.

Now I'm on my 3rd alternator and begun wondering if there's something else causing the alternator to fail (a short in the engine fan circuit or AC coil)... Can you point me to a method to test for such shorts?

Finally I've seen that the IGN Fuse cover has melted without the 15A fuse failing. Do you have any idea what would cause such behavior/high IGN fuse temperature?

THe a/c blower requires 25 amps on high setting, which is enough to cook the motor if running for long... failed winding insulation leading to a short circuit between adjacent morot coils will make the motor ask for even more current. I'.d test the blower motor amps on high.
Heat is bad on everything electrical and electronics, period.
Again, GM components, original or replacemnt, are pieces of scrap. IF you can find Bocsh replacement components, go for that.
A for the 15 ign fuse, check that out:
www.avigex.ca/xport/ignfuse31.jpg