My inside unit freezes up after running for about an hour. For the past three years, at the beginning of summer we have to have it recharged. Last year it was low three pounds. I have had three different companies come out and inspect and they say they cannot find any leaks. Where is the coolant going? Unit is only about 4 years old. After we get if charged it works all summer, and at the beginning of the next same old problem. Its getting expensive to replace coolant every year. Anyone got any suggestions?

I would say you have a small leak in the coil. It is still under warranty if it is less then 5 years old. I would tell them you want a new coil. If not you can add a can of stop leak to the system.

What brand is your unit?