About a month ago, we noticed the a/c was blowing but not cooling. We called out a tech, they said it was low on coolant, added it and we were back in business. About 2 weeks later, stopped cooling again. Came back and did a leak check. Had trouble locating one, but eventually came back and said it was coming from under the house and they needed to do a line set. As they couldn't do it until the following week, we called another company for a second opinion , as the house and until are all only 4 years old. The second tech said there was no leak, and in fact he had to release coolant as it was overcharged. He cited a bad expansion valve and replaced it. Back in business. Stops working 2 days later. Tech comes back and says the part was bad, replaced it, and back in business. Now 2 days later, it is not working again. I don't know anything about these things, so I am at their mercy. I am now sitting here in the 80 degree house waiting for them to return , yet again. Any ideas? Very frustrated.