GMC Repair: AC/Fan control, vacuum actuators, vacuum lines

Question
I own a GMC K1500 Z71 Pickup, it has a 350 Vortec and auto if it matters. The A/C has always worked when I need it. Lately, my son installed a custom stereo, and now the switch controlling where the blower is directed does nothing and air only comes out of the floor vents. Big problem if not fixed by winter. The biggest problem is when the A/C button is pushed in all the way, the light will not show its running, and the A/C is not kicking in. I have checked all the connections and wiggled them, nothing is loose. Now i have heard of a vaccum line being disconnected, however only electrical wires are connected to the head unit where you change the settings at, and i do not know which step to take after wiggling all wires and making sure everything is connected. Help would be appreciated.

Thanks,

Tyler

Answer
Hi
With a Vortec I am guessing a 95-99 year model truck?
If so there is no vacuum lines and or vacuum actuators for the HVAC system.
It REALLY sounds like 1 of two things..
1) Logic lock... You Could unhook BOTH  the negative AND positive battery cables. WITH THEM NOT ON BATTERY, touch them together for 30 seconds.
Then hook the negitive first, then the positive...if still acts up,
2) You'll need the HVAC controller.
Also with an aftermarket custom radio, you MAY want to disconnect it FIRST before doing this procedure.
I Hope this helps.
JUST ADVICE from experience.
Good Luck
Pawl