It has an air bubble in the line at the pump or air in the pump, ideally the line should come from the thru hull
and have a slight uphill run all the way to the AC with no point being as low or lower than the pump, most installations don’t meet that requirement and when the boat
is hauled the water drains out of course and when relaunched the bubble forms.
Only way I have ever had success with it Is to loosen the hose that comes out of the pump until it sprays water and then retighten it, you don’t need to take it off, just loosen it, and it works better if the pump is running, but you have to be quick because the AC will soon overheat without cooling
water and throw a code. So loosen the line and then turn the AC on, the pump is easy to tell it’s running because you can feel it.
You should be good for the year, but sometimes when heeled over the system will drain again and then your back to bleeding it again.
I have two AC’s one never, ever has a problem and the other one does. I need to relocate the pump higher on the one that has a problem, but of course still be below water line.
The whole line coming from the thru hull
to the AC should all be slightly uphill.
On my instal the strainer is slightly above the pump, I need to raise the pump or lower the strainer or both.