Our heat pump keeps clicking on and off before staying on. It did the samething about 2 years ago. We had someone come and clean it and clean the water out of the pan under the house, it was real bad. Everything has worked fine until recently and it started it again. My husband cleaned it all again, and even fixed the drain pipe so the water would run out better. It seemed fine for a few days and it's doing it again now. The entire system was put in when we built the house 9 years ago. As far as the heating or cooling, it works fine after it decides to stay on.
Thanks for any and all help.
Cindy

It could be a defective or out of range pressure switch.
If there is a float switch or a safety overflow switch on the drain pan that could also be a problem
There are to many other items to actually list.
I suggest you get a On site inspection by a HVAC company before it gets hot and the unit completely stops working.
This time watch and see what the service tech does.