When the Air Conditioner is on it works great, but it only stays on for about 20 min then blows warm air. After blowing warm air for about 5 min it turns back on. Last summer I tried to get it fixed, they checked the compresser and said it was great, so they then replaced some hoses and recharged the system. But it did no good. They said they didn't know what was wrong. Has anyone had this problem and had it fixed? Thank You.