400ss A/C getting air in line when running?
 

I have 400ss and anytime I run my boat lately the A/C gets air in the line and needs to be bled through the valve on the outlet of the A/C pump. This is happening even when I turn the A/C off before running the boat. Has anyone dealt with this before? I have had issues with the A/C needing to be bled every so often but now its every time I use the boat.

Thanks

does your boat come out of the water for storage or on a lift?

I had that problem with the AC in a 382. Stepped hull lets air in there and running seems to create a vacuum effect that creates an air pocket the pump can't overcome. I started closing the seacock when I wasn't using the AC. It was a little bit of trouble but it solved the problem.

My boat is kept in the water. The A/C hasn't had an issue when running at the dock.

I can see how the stepped hull could create this issue, but Its only started acting like this way this summer. Its a PITA to open the hatch after each run to bleed the valve, although it only takes a few second to actually bleed and this solves the problem. Im hoping theres something I can do to resolve this.

You may want to check the thru hull and see if there is a buildup of scum, barnacles, anything that can grow if you normally leave the boat in the water. If it was fine before, growth is the only variable that can change anything. What year 400 is it? Not that the year matters, only asking because its probably that long since the thru-hull has been cleaned or inspected.

Thats a good place to check. I do have the bottom cleaned about once a month and I know the diver is very thorough but I have not asked him to look at the thru-hull fittings.

As i get these calls almost daily here at work i can possibly give a little insight....
First make sure the pump is below the water line of the boat as they are not self priming pumps (assuming this is a March pump which i'd guess some 80% are) The lower in the bilge you have it mounted the better the water pressure will force its way into the pump and keep it primed... also ideally the pump should be mounted horizontal with the outlet facing straight up....you have to keep in mind that air will seek its highest point and you want to have the outlet at the highest point to let the air out of the pump.

Second make sure you don't have any cracked fittings that are letting air into the pump.

Third make sure the run from the pump to the A/C system is straight (little if any dips causing a water trap) and make sure you have a good rise so when the system is turned off the water will siphon back to the pump and level itself off. That's probably the biggest issue most boaters face....when new the lines are stiff and if not properly supported every so often you will get low spots and they will act like a trap/plug....if water siphons back to the pump and you get air in the system that plug will not let water back into the pump on next start and thus needing a bleed. If you cant fix the lines dues to bulkheads etc in the way then i have advised boaters to install a "T" fitting at the discharge of the pump with one side of the "T" having a run of tubing and a valve on the end you can run up under the gunnel somewhere so you can crack the valve quickly without having to go down into the engine compartment to do it....

Hope that helps a little bit,,,

400 SS a/c
 

We used to have the same problem on new boats at speed. we solve it by cutting a small groove about 3/8 wide on the bow facing face of the a/c thru-hull. At speed it would make an air bubble over the thru-hull losing prime.

These sound like some good suggestions. The pump comes mounted from the factory in a horizontal position and pretty much as low as it can be.

You cut a groove in the thru-hull fitting itself? Do you have any pictures of one you did this to?

I've seen the groove in the thru hull flange, I assumed it was to ram some water into the inlet, never thought much about it, it's cast in on my thru hull.
The O-Ring on the sea strainer might be giving up, did you check that? I had mine out recently, seating it correctly was a PITA until I cleaned the sealing face thoroughly. Any water on the outside of the strainer will tell you it can also get air.
I can't run the AC on my 370SS at all on a plane, the pump gets air too easily from the steps ahead of it.