Yeah I work at a Chevy store, so the guy who's going to look at it today is pretty good with that kind of stuff. He's helped me with some oddball issues on my C5 Corvette too. Hopefully he'll have time to get to it today and I can report back!
BTW - looked at your signature - I'd KILL for one of those DOHC 5-speed Achievas
Fwiw, with the GM 2nd-rate wire/copper that was used, often the wire break is hidden inside the wiring jacket.
The ABS wires that go from the frame to front suspension are a great example.
Also, as I mentioned, the garbage wire looms often fall apart, leading to rubbing wires, leading to a broken wire. That almost happened to the CPS sensor wires on my 2000 Old's LX5 engine.
In my 2000 Olds, I have a power feed that has a break in it. It effects my HVAC electronic control and speed control (?and radio?). I used a spare unused power feed in the fuse box, and jumpered it to the bad power feed line (via an inline fuse). It's been fine for many years, and I didn't waste 4-10+ hours taking apart the dash/etc just to find exactly where the break is.
The mechanic that used to work at a nearby local garage was a GM dealer mechanic for many years. It was great. If I didn't have time, or feel like screwing with something, I'd just drop my car off there. He is a great guy. He got sick of being a dealer mechanic, and went the route of a being a local garage mechanic. He was straight forward, treated every customer with respect, and is a nice person. He was even knowledgeable about the Quad4 in my '92 Olds Achieva. :) I don't know where he went after that local garage changed ownership (former owner retired at ~70 years old).
The mechanic that is at now that local garage is a Honda and Toyota expert, Which is good for the garage, since those are the most common vehicles they get. But, as for my GM cars or Mustang, he knows very little about the common problems/issues with any of those cars. 😐
I had this same problem with my 97 grand prix. The fans ran until I kicked on the AC then the fans would stop. I got passed off threw some crap around the garage. After calming down I noticed the harness that connects the 2 fans together was toasted from the exhaust manifold. Replaced that and it fixed my issue
I'm not saying that this is for sure your issue but it's worth a easy inspection.
I can't upload a photo of it but it's in the middle of the fans, connected to the shroud close to cylinder 3