I've never had to prime an AC pump.
Probably because the storage yard is 10 miles away from my marina and I have never tried to run my AC when they set the boat in the water, I wait until I am at my dock to do it. Driving the boat forces water through the scoop strainer (as long as the seacock is open of course) and takes care of priming it.
On our current boat, the pump is below the water line, problem solved. Suggest you go for a boat ride, might be all it takes. If not, you may have to get a little more creative. I've heard of guys back filling the system by sticking a garden hose via some homemade adaptor into the thru hull discharge. If you have two AC's, you will most likely have to plug the thru hull you're not sticking the hose in.

 

The pump is usually at or very near the level of the sea water strainer. Take the lid off the strainer. Open the seacock a bit to allow water to flow in. It will flow to the pump. Close seacock, replace lid.

Alternatively, you could leave the seacock closed and pour water in into the strainer so it flows into the hose to the pump. Could use a hose for this.

 

The pump is usually at or very near the level of the sea water strainer. Take the lid off the strainer. Open the seacock a bit to allow water to flow in. It will flow to the pump. Close seacock, replace lid.

Alternatively, you could leave the seacock closed and pour water in into the strainer so it flows into the hose to the pump. Could use a hose for this.

THIS

If you know the boat is coming out of the water than close the seacock(s).

 

If your thru hull "water out" is easily accessible force water into it and watch the bubbles come out from under the stern. Once the bubbles have cleared - it's purged.

 

My first time doing this took little effort. I grabbed my wet vac from the dock box, put the hose up to the thru hull, and whola, it sucked the water out and started flowing! Literally two minutes and no climbing into the bilge

 

I used to pour water from ac to pump. The unit in cabin was higher than pump in bilge.

 

Agree with JB. Backflow the pump.

 

There is a plug on my pump. I removed it till water came out . Then realized I was stuck under my floor. . LOL

 

I put a tee before the pump for flushing the seacock out and it doubles as a prime if needed. The tee has a valve on top of it allowing a hose connection.

 

Cool thanks for the suggestions, I’ve been loosening the hose on the outflow side of the pump for years but figured there has to be an easier way.

 

If you have Groco strainers, there are flush caps available that greatly simplify flushing and priming. I have a set on my generator and main engine. This version is bronze with a ball valve and threaded port, meant to be used when the engine is in service (vs. the plastic caps that are for temp use only). I use these to flush my generator and engine after every use; they could easily be used to also flush/prime an AC system.

 

Vacuum on discharge

 

You put a vacuum on the thru hull on side of boat?

 

Damn 300$ a piece that’s steep lol

 

I think we need a tutorial on how to build those flush caps lol

 

The flush caps are not that expensive.
https://www.amazon.com/Trac-Ecological-Flushing-Groco-500-750/dp/B01C04H7U4/ref=sr_1_1?adgrpid=1343603781840908&hvadid=83975484584942&hvbmt=be&hvdev=c&hvlocphy=164334&hvnetw=o&hvqmt=e&hvtargid=kwd-83975599281132:loc-190&hydadcr=6588_13218672&keywords=groco+flush+cap&qid=1688751157&sr=8-1

Or you can buy a regular cap, drill it, and install a plastic bulkhead fitting in the hole.
https://www.amazon.com/Groco-ARG-Strainer-Cap44/dp/B074KKYQQZ/ref=sr_1_5?adgrpid=1343603781840908&hvadid=83975484584942&hvbmt=be&hvdev=c&hvlocphy=164334&hvnetw=o&hvqmt=e&hvtargid=kwd-83975599281132:loc-190&hydadcr=6588_13218672&keywords=groco+flush+cap&qid=1688751269&sr=8-5

 

While I have the flush caps for winterizing, I just can’t imagine anything faster that the vacuum on the thru hull. I will say I like the idea of putting the hose in the thru hull but I never tried it. Just be sure it’s not the sink thru hull

 

Yesterday I went to boat for first time in weeks and mission one was to open a/c seacock and get a/c running. As expected, no prime so we pulled out the trusty vacuum as I bragged about, expecting this to take seconds. Well the dam vacuum burnt out. So I remember reading the back flow hose trick and in 1 minute I heard the bubbles under the boat and voila - water flowing nicely .

Thanks for the tip - may be my new go to...

 

Just an FYI. Most all quick disconnects are very volume restrictive.

 

True. The ones I have are about a full flow as you can get. I only use the flush cap on the main when it’s at idle. Rust gives enough flow to avoid an issue. I also don’t close the seacock so no risk of cooling water starvation.

 

I have the same seaboard marine caps that @b_arrington has. Mine has the fitting tapped and soldered in place. Use them religiously, but hook up the hose directly. No issues whatsoever.

 

Getting back to the original question I placed a tee in the line after the pump to a line that is run above the waterline with a 90 degree valve. After cleaning the AC system I just open that line while the pump is off to remove the air in the line.

 

As long as my boat is moving in the water, the ac primes itself.

 

I was hoping this would be a good thread lol