We have a whole house fan too. It doesn't do any good though when the temp outside is near the same temp as inside. It was like 82 outside last night and 88 inside. When the temps are so close you can run it on high for hours and hours and it barely cools down inside. There needs to be more like 10+ degree difference for those to work very well.
Ours has a timer so I set it to run until 6am and it cooled things down a little. It works really great in the spring and fall, but not so great in the summer when it doesnt cool down very much until almost sunrise. We got suckered into a more expensive "quiter" model so it was like $500 but I think there was a $200 rebate. It's really not any quieter that I can tell. The remote control though with a timer is nice. That way there doesnt need to be a switch on a wall that friends flip on accident and turn on with all the windows closed. I had that happen at my last home and it sucked in a lot of ash from the fireplace onto the carpet.
Near the end of the day my wife found a company from out of town who had someone available to come out. We can get a new coil for like $7k or a new unit for $11k. Needless to say we're going to get more quotes. I always thought these things only cost like $3-4k + installation, so maybe $4-6k. So I was quite shocked. It was a Lenox, I'm not sure if that brand is more expensive.