How to flush A/C water lines?

Sum Escape

Sum Escape

Member
Apr 7, 2009
393
West Florida
Boat Info
2020 Tiara 53 Flybridge
Engines
CAT C 12.9 1000 HP Straight Shaft
Perhaps I am not searching correctly but I could not find a description of how to flush sediment from A/C water lines. My forward and cockpit units have a restricted water flow (salon unit is fine) and given we slip in waters with pretty heavy sediment content I am thinking sediment build up in the lines may be the issue. Can I just disconnect the line "downstream" of AC circulating pump and backflush from thru hull fitting? Thanks
 
I blow my AC out with my Compressor at 100 PSI... On my boat you can blow my the pump... This is not the case with water pump... BTW I put a hose connection betweein the pump and the strainer... I blow both ways....
 
rcknecht said:
I blow my AC out with my Compressor at 100 PSI... On my boat you can blow my the pump... This is not the case with water pump... BTW I put a hose connection betweein the pump and the strainer... I blow both ways....
Click to expand...


If you could take a picture of that connection after the thaw that would be sweet!
 
To answer your question specifically, yes. I have to ask, what do you mean by sediment? If it is a "silt" build up, are you cleaning the the strainers ofter enough to account for the sediment? BTDT.

I have seen folks backflush the system with a garden hose against the thru hull to get the strainers flushed. I have never done this. "Stuff" going through the AC pump one way, once is enough for me.
 
Other than cleaning the strainer basket, I haven't had that issue. But I do add Bromide tablets (swimming pool supplies) in the basket to keep algea growth in check during summer months.
 
Funny. Just did this a few minutes ago. What I do is have the system running, and backflush from the thru hull fittings, using a garden hose to a 3/8 or 1/2 barb fitting (depends on your thru hull fitting). The splashing is minimal. I backflush for 10 seconds or so, and then let the pump pressure push the "silt" out. As soon as the water is clear again, I repeat. Do this about 4 times for each thru hull. This is of course AFTER cleaning the strainer and occasionally backflushing from the strainer to the inlet thru hull. In my area, the silt is algae build up in the hoses. Bromide helps, but does not eliminate this condition in my waters.
 
If it's hard growth in the lines, just like the raw water side of your engines' cooling systems, you can flush with diluted muriatic acid, or Rydlyme Marine. Put the stuff in a bucket with a small pump and create a loop with the lines to circulate the solution.
 
Never had as issue with silt here in the Great Lakes. Just force the water out with compressed air when in dry dock at the end of the season, then clean the strainer.
 
fwebster said:
Can I ask why you guys are back flushing? Doesn't that just force all the crud back into the compressor coil, the pump and manifold?
Click to expand...

Guess that would depend on where the crap is (if there is any), before or after the A/C coils.:huh:
 
Since its a very short, straight shot from the coil to the thru-hull, its a real good guess that the crud is in the coil. So my question still stands.........why force all the crud back thru the pump and manifold?
 
fwebster said:
Since its a very short, straight shot from the coil to the thru-hull, its a real good guess that the crud is in the coil. So my question still stands.........why force all the crud back thru the pump and manifold?
Click to expand...
My understanding is that with our northern boats being stored for six plus months, the silt and crud collects/settles and can cause restrictions as things sit idle. Your concern is why I am thinking about flushing downstream of the pump. So I either back flush with the line disconnected at the pump (I don't want crud in there!) or flush from the disconnected pump in the normal flow direction. The maniofold probably already has the crud in there so which flushing direction will get it out the best? Further thoughts from anyone? Thanks
 
I'm going to take a step back here...
How are the three units plumbed- are the forward and cockpit a/c's (the ones with the problem) served by the same pump, with the cockpit a/c served by a separate pump? Or, are all three units served by the single pump?

If the latter is the case, do you have ball valves installed in the lines to regulate the flow of water to each unit?

My 390 did not- and once I installed them I was able to properly balance the flow to each unit.
 
fwebster said:
Can I ask why you guys are back flushing? Doesn't that just force all the crud back into the compressor coil, the pump and manifold?
Click to expand...

I do my method because it is quick, doesn't require a screwdriver, and doesn't leave a mess in the bilge.
 
Put a T in the line between the sea cock and the strainer.........the strainer has an ell, remove it and replace with a 'T"....put a ball valve and a hose connection on the 3rd side of the "T". When you flush, hook up a hose to the T and let her go full stream.

The airconditioner can be on or off. Since the pump has a magnetic impeller it free-wheels with the flow from the hose. The added pressure from the "city" water hose will flush most of the crud out of the system.......any that it won't flush is from marine growth adhering to the inside of the lines which requires an acid flush to clean out.

The above method flushes the short way, doesn't require disassembling anything, makes no mess in the boat and is much easier than getting to the a/c outlets with a hose to back flush.
 
I used to keep my boat up on a river in the summer that had a ridiculous amount of sediment in the water. It was nearly fresh water so I didn't have the salt issues to deal with but I'm not so sure keeping the sediment cleaned out of pumps and heat exchangers isn't harder. The AC and pumps were always on in the summer and the strainer would collect so much sediment that lily pad seeds and acorns would start to take root in the thing... cleaning roots out of the stainless strainer screens is not easy.

I could always tell when the main salon pump circuit would get blockage as the forward stateroom water discharge looked like a 60 year-old man with a bad prostate problem trying to pee. I ended up flushing the circuit with Rydlyme every 1-2 years as it does a decent job removing all the organic crap and sediment as well as scale. After a flush, I always had good flow out of the forward stateroom. I have a pump kit and would plumb it up and let it circulate for about 2 hours.

Last year I had the pump start to make some funny noise and I pulled it out and the sediment had caked and hardened on the magnetic sleeve as shown here:

DSC_0105-1.jpg


The internal magnet could not spin freely because of the caked on gunk and was slowing down the water flow. In hind sight, I probably should have been pulling that pump head off every year and cleaning it out... I ended up putting a new pump in because I didn't want to screw around with the old one... I did clean the old one up after the fact and plug it in at the shop and it works just fine now... so I have a spare.

I bring this up as you may want to pull that head apart and inspect it if you think you have been in a lot of sediment for some time... and if you are going to be there, you may want to invest in a recirculating pump kit for flushing... All your heat exchangers will love you for it.

Gotta love muddy water...
 
Last edited:
Four Suns,

Thanks , you hit the issue right on the head! Lots of river sediment. I'll take a closer look next time I get to heated storage. Also, its nice to read your posts again...thanks.
 
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