2003 Jeep Cherokee power steering

I bought this used Jeep Cherokee a few days ago. The last two days have been around 20 degrees. The problem I am having is when I first go to take off there is no power steering. It takes it a min. then I get power steering. I have checked and see no leaks and the fluid is in the good range. Does temp. affect the power steering or do I need to look at replacing the power steering pump?