I don't keep Mountain Kings nor do I live in Southern California, but I have some ideas.
If the air conditioner is not doing enough, or you keep other species that require higher temperatures, you have other choices.
Obviously, you could cool the room to the desired temps for your mountain kings and use supplemental heat to raise temps in other cages. Either UTH's or radiant heat panels will raise temps with minimal effects on the ambient temps in the room.
If the air condition is not quite doing it's job you could purchase an ultrasonic humidifier and run aquarium tubing off of the resevoir. Then direct the tubing into your mountain king cages specifically and the evaporate cooling will bring the cage temps down considerably.
You'll have to make sure there is sufficient ventilation in your Mountain King cages as to avoid excessive substrate moisture.
Lastly, if you're just trying to bring the temps down in the room a bit more than the AC can handle, consider building a swamp cooler.
BigTatto posted a great design for this on the old caging forum. He strung burlap over a PVC frame and down into a large tub of water. The water wicked up the burlap and he had a box-fan blowing on the burlap. This caused evaporative cooling in the entire room and helped cool things down.
I hope I remember his design correctly.
Like I said, a lot of this depends on exactly what you're trying to do and what other species you keep.
for those of you that keep mtn.kings in so. cal. How do you keep the temps cool during the summer months? I installed an air conditioner in my snake "shed" (the wife thinks I'm nuts)but I am wondering if there is a more cost efficient method of keeping cool here in L.A. county. I need to keep the temps no higher then 82 degrees for many of my mt species. Any response would be appreciated.