Noticed electrical system voltage dropping whenever the HVAC system is on, so I checked current going to the blower fan and it's 17.1 amps at high speed. This seems like a lot to me for what it does (almost 240 watts at 14V); has anyone measured the current on a good blower?

 

That sounds about right to me.

 

I second that, my GM products are all 15-20 amps on high. The high speed wiring typically goes through a high blower relay and is wired with a very heavy gauge wire to keep the circuit from overheating.