Heya! "Cliff-notes" version of the story, here. Bought a 98 Blazer in February of this year. 98 Blazer LT, LOADED, 115k original, one-owner, everything worked (except AC nedded a charge, and lights in AC head/control unit didn't work....rest of switch was fine).

Started getting warmer around here a couple weeks ago, so I decided to seal and charge the AC. Took almost a full can of freon to top it off, no problem. Got it within spec, only to discover that my computer controlled ac/climate control head (switch panel) was apparently DEAD! No lights, no buttons working, no fan, no defrost, no AC, no rear defrost. All functions controlled by the "head" unit appear to be out.

Checked all "applicable" fuses and relays with no luck. The ONLY thing I haven't done is to actually pull the switch head assembly and check the connections. That's next when I have a few minutes to spare.

I've heard of several reports of people having intermittent or partial function problems with this switch/control assembly, but not TOTAL sudden failure!? Any ideas folks?? In the mean-time, I'll be looking for the opportunity to pull mine out of the dash and check the connections. After that, I'm stumped!! HELP!!

 

I have a 98 LT also with the same unit as you. I can't answer your issue, but I can tell you I have had to a wiper pulse board, & headlite switch. So I think your on the right track with the switches.
Please post what you find so if mine goes out I might have a better idea where to go. I sure dislike these auto climate control units, I which I had a manual like my 97 LS had.