If the antenna is aimed at the mountain... how does interference within your home cause issues? What kind of proximity is the antenna to the A/C fan motor? I think the only way it would make sense for your connection to have issues when the A/C is running is if a strong electromagnetic component of the unit were in fairly close proximity. Those motors can definitely do that. If that's the cause, relocate your antenna further away from the motor. Even just an extra 5 feet away can make a big difference.
Get that thing up in the air on a pole!
... hey seriously, if my only choice was wireless internet, that's what my house would look like.