AC water flow

HGM

HGM

New Member
Sep 16, 2010
77
Chesapeake Bay
Boat Info
1991 350 Sundancer
Engines
twin 454
I am having a problem with water flow for the AC units. I started both AC units this weekend and had no water flow. I had replaced the hose from the sea cock to the strainer and to the pump. I primed the pump and strainer and got minimal flow out of the aft unit only. I replaced the impeller but had no change. I than disconnected the hose coming out of the pump and ran water from a garden hose through the units. I had good flow so there is no blockage through the units. I blew water back through the sea cock to make sure the inlet was clear. I replaced the cap seal on the strainer. If I need to replace the pump I will but I have never seen a pump loose efficiency like this.
 
When you refer to the AC units, are you referring to the shower and sink? My sink and shower have have no flow, and Im curious to know what is the fix. Is this the experience you're having?
 
I am referring to the cooling water that flows through the air conditioning units.
 
recently I had the same problem. sea cock used to remain open. this time I pulled the hose and stuck my finger in the seacock opening. tremendous amount of scale buildup. the diameter of the opening was probably the size of a dime. I chipped away at it and then did the same with all of the seacocks as a precaution. seacocks now stay closed when I'm away from boat and diver can keep the bottom part clear.
 
How did you prime the pump? I had the same issue this year so I had to remove the hose at the strainer inlet, hook up a hose to a 5 gal, container of water (gravity feed) and finally the pump primed and started pumping. I then reconnected the hose from seacock to strainer and all is now OK. The pump is not self priming and is difficult to get working when dry.
 
Last edited:
HGM said:
I am having a problem with water flow for the AC units. I started both AC units this weekend and had no water flow. I had replaced the hose from the sea cock to the strainer and to the pump. I primed the pump and strainer and got minimal flow out of the aft unit only. I replaced the impeller but had no change. I than disconnected the hose coming out of the pump and ran water from a garden hose through the units. I had good flow so there is no blockage through the units. I blew water back through the sea cock to make sure the inlet was clear. I replaced the cap seal on the strainer. If I need to replace the pump I will but I have never seen a pump loose efficiency like this.
Click to expand...

From all the things you've tried I don't see the part where you would disconnect the hose after the pump to see if you have a good flow and make sure the pump is pumping or not.
 
typical install is that the pump is installed at or below the waterline. The pump chamber should be full of water and self prime.

Has the pump been moved? R U double clamped from sea cock to pump inlet to rule out pulling air .
 
I did not run the pump with the outlet hose disconnected. I was getting some flow from the pump through the aft discharge port. Not good flow but enough to operate the unit. I primed the pump by opening the strainer and than opening and closing the sea cock to flood the strainer and the line. I ran water back through the sea cock but did not check for a blockage. I believe the pump is in it's original location. It is below the water line.
 
I'd first establish that you're getting flow at the pump by doing what Alex said. If you get good flow at the pump, you likely have an obstruction further forward. Leave the hose disconnected at the pump and stick a garden hose into each overboard discharge and see if flow is strong back at the disconnected end (at the pump).
 
I found and easier way to prime the pump. I shut the sea cock open it up clean the strainer. Then I have the strainer placed right next to the valve so I can replace it quickly. With the valve closed I put the external water hose in the open sea cock while trying to seal it with an towel or rag and fill it up. Then remove the hose and quickly replace the strainer and secure the sea cock cover. You need to do this quickly because the water you just put in the system will want to return to you. Some will however enough will remain to prime the pump. Open the sea cock and there you go.
You can also remove the hose as recommended but I believe in letting sleeping dogs alone, continually removing this hose each time to prime the pump may in time create a leak. IMO
 
you can also prime the pump by loosening a bolt and have it draw a little air. This will then creat vacuum once you tighten. I did this last year and it worked great without a lot of water spraying.
 
With the boat in the water it will be very difficult to back flush the lines. I did use a garden hose at the pump outlet hose forward and had very good flow at both outlets.
 
Could be that you have a bad impeller. I kept getting a LO PS reading - I replaced the pump and it solved the problem. I have heard you can replace the impeller but I didn't much research on it. I figured old boat, old pump, might as well replace the whole thing.
 
I did replace the impeller with no improvement. Today I bought a section of hose to temporally bypass the strainer. If needed i have a reseal kit for the strainer. I am going to check for a restriction in the sea cock. If i don't find anything I guess i will change the pump.
 
I have never had this pump apart so I'm just speculating.
Is it possible that the impeller is spinning on the shaft?
When you took the pump apart was there a gasket or O-Ring? If so did you replace it?
Could there be a hairline crack on the pump allowing air to be sucked in?
Did you remove the pump to replace the impeller? If so did you rewire it correctly? It's not spinning backwards is it?
Did you compare the new impeller and the old impeller side by side to be sure you got the right one?
Some more food for thought. Good luck.
 
Pump is a mag drive, impellers were identical and replaced without removing disconnecting the pump. Seal is an o ring that was in excellent shape. Don't know about housing or hose barb.
 
HGM
Where'd you locate the impeller?
 
I believe the impellar is plastic (almost like a fish tank pump impeller) and rarely goes bad unlike the genny impeller. Since I keep my boat on a lift I lose prime everytime I lift it out of the water. The easiest way for me to prime the AC system is when i have the boat out I turn on the genny then at idle speed or a little bit faster I turn on the AC unit. This forces water into the strainer and primes everytime. I could close the seacock before I left my boat out of the water but that becomes a PITA.
 
I finally got flow. After checking everything I could think of, I changed the pump. Everything is working great. I have never seen a pump with a hard impeller loose flow like this. Thanks for all the help.
 
You must log in or register to reply here.

Forum statistics

Threads
113,228
Messages
1,428,953
Members
61,120
Latest member
jingenio
Back
Top