Check engine light

I own a 2000 Blazer. Recently, I noticed a clicking sound coming from behind the dash in the general area of the Steering column. It almost sounds like a switch being turned on and off. I thought that perhaps it was a short so I looked in the Instrument Fuse Panel. I noticed that the 2 fuses for the HVAC were missing, so I replaced them. When I replaced the fuses, the Check Engine Light came on. First of all, What is an HVAC and, what does it do? Second, Why would it be tripping the Check Engine Light? It this a sensor Problem that I could deal with Myself? I really need help on this. I LOVE my blazer and I need to fix it up. Please Help!!!!!!!!!

HVAC stands for Heater Vent Air Conditioner.