If you are experiencing this problem in the cooling mode during the summer, you should probably call for service. This is mostly a winter-time heating complaint.
Just like the previous complaint of the heat pump blowing cold air, sometimes the customer just thinks it runs all the time because they aren't used to a heat pump and how they work. In extremely cold weather, a properly working heat pump will run almost continuously. That is the way they were designed to work.
Now, if it isn't extremely cold and suddenly your heat pump just seems to run all the time, this indicates a problem. Along with this usually comes a high electric bill, lower supply temperatures, and sometimes icing of the outdoor unit.
Below is a list of possible causes.