I just went through this with our Raycor primary on our Yanmar
3GM30F. My primary is located slightly above the fuel line. At first, when I put the filter back together, the Raycor filter and bowl were empty. I tried bleeding the system by pumping the manual pump lever. I didn't see any fuel/air escaping from the first bleed screw nor did I feel that fuel was flowing. The manual pump felt limp.
What I did was disconnect the fuel input line from the Raycor filter and drain about 1/2 fuel into the filter/bowl. All I had to do was move the filter/bowl below the level of the fuel line and fuel drained naturally. I reassembled and repeated the pump/bleed process. This time I definitely felt pressure on the pump and saw fuel/air escaping from the bleed screw.
When I did the secondary filter, which is located below the heat exchanger
, I also did not fill the filter with fuel. This time, the pump did circulate fuel and I could bleed from the second bleed screw.
Overall, I was pleasantly surprised at how easy it was to bleed the air from the system. Afterwards, I ran the engine about 20 minutes just to make sure there was no air remaining in the system.
My feeling is that my primary needed to be partially filled to circulate fuel; while the secondary did not. As skipmac said, probably due to the height/location of the filters.
A couple other things I've learned - to minimize spilling diesel I would try to unscrew the filter and bowl together. I didn't want to reuse the diesel as it had black sediment. It might be useful to have a 1/2 pint of clean diesel to refill the filter/bowl. In my case, draining fuel worked well.