05 chevy trailblazer overheating

I have a 2005 chevy trailblazer v6 4.2. Everytime i drive for
about 20mins with the a\c on it starts to overheat it says oil
pressure low shut off engine. I had the valve cover gasket
changed because it was leaking oil. The guy said it was
from the person who put the old one sliced the gasket  
when they replaced the top. The check engine light was on
and when i tested it it said a code that had to do with the ac
clutch also pedal accelerator and vvt and when i looked
under my hood i noticed the wires were cut so my brother
put wired it back togerther and he diconnected battery and
check engine light went off and the car ran great for 2 days
and didnt overheat. If the check engine light went off could
those still be possible problems. It isnt leaking oil. And the
reservoir starts bubbling when overheating but isnt leaking.