ac replacement

I just put on an atwood 15,000 with a heat pump. It replaced a 13,500 . The atwood is quieter and blows more air. Really like it on acnd. It cools the front of the coach like it has never been cool before. That said I hate the way it works on heat pump. I'm on my second one, replaced the first under warranty because I didn't like how it worked, and the second works just like the first. The air temp will get hot, but as soon as it does it shuts off. It takes forever to raise the inside temp. It will only work if outside temp is an over about 45°f. About might be 48 sometimes. I'm still hopeing to get it better, but I think the controls just work that way. Atwood thinks so too and for heating it is a waste. For acnd it's great.