I have the exact same car. I had the same problem, for a number of years. I got two coolant flushes, and an air conditioner kit. Then toward the end of 2013 my engine overheated. Apparently my water pump was leaking. It's under the timing belt, so perhaps it's hard to see (or just expensive). I think I read that it requires the removal of the timing belt. So you might have to get a new timing belt at the same time. I did, along with radiator and several sets of hoses. Ask the shop to look at your water pump. If it's leaking, it can interfere with your air conditioning.