A/C condensation question

Ezsteps

Ezsteps

Well-Known Member
Nov 14, 2015
1,341
Lake St. Clair-- Michigan (MacRay Harbor)
Boat Info
1999 400 Sundancer, YL310 Zodiac, MX 335 Novurania
Engines
7.4 Mercuisers Horizons 380 hp ea., 9.9 hp Mercury, 30 Yamaha
I have a 99' 400 Sundancer. The last couple of weekends I have noticed that my Shower/Air Conditioning sump pump would cycle every now and then (which seemed unusual as I have never noticed this). After taking the top off the sump box I noticed my A/C hose going into it was wet. I check the unit under the front bunk and the pan had quite a bit of water in it and the unit itself seemed to have excessive condensation on it. I then checked the aft A/C unit and it was dry. I know that humidity is a major cause of condensation but I don't get why my forward is wet and the aft is dry. My question is: What else could be causing excessive condensation on my forward A/C unit? I should add that I have checked my vent and filters and they are all clean as well. This is my third season with the boat and I have never noticed my pump cycling unless we were taking a shower. TIA
 
Mine will kick on and pump out the Cindi station... which is good.

My 34 baja with AC dumped it into the forward bilge.... right beside the shower sump, causing moldy bilge....
 
Ezsteps said:
I have a 99' 400 Sundancer. The last couple of weekends I have noticed that my Shower/Air Conditioning sump pump would cycle every now and then (which seemed unusual as I have never noticed this). After taking the top off the sump box I noticed my A/C hose going into it was wet. I check the unit under the front bunk and the pan had quite a bit of water in it and the unit itself seemed to have excessive condensation on it. I then checked the aft A/C unit and it was dry. I know that humidity is a major cause of condensation but I don't get why my forward is wet and the aft is dry. My question is: What else could be causing excessive condensation on my forward A/C unit? I should add that I have checked my vent and filters and they are all clean as well. This is my third season with the boat and I have never noticed my pump cycling unless we were taking a shower. TIA
Click to expand...

Your aft AC is draining correctly, your forward AC has some build up in the drain line.

Take a shop vac, open the shower sump (you do clean the shower sump on a regular basis, correct?).

Place the vac hose over the opening for each AC condensation drain and suck the moisture and what ever else is in there out.

My previous boat was a 400 EC, and in the summer my shower sump was cycling every 15-20 minutes from AC condensation, which is normal for here.
 
Thanks CaptRonn, I will try this when I get to the boat this weekend. Yes I check the screen a couple times a season and clean out when necessary.
 
Reminds me I need to clean my sump, as ai have a week long trip about to take and shower will be used.
 
Ezsteps said:
Thanks CaptRonn, I will try this when I get to the boat this weekend. Yes I check the screen a couple times a season and clean out when necessary.
Click to expand...
Let me know if this works for you. I have the exact same issue. I've had instances where the build up in the pan under the bed spilled into the floor hatch while underway. Wasn't sure how to clean it from the top side.
 
THJeff said:
Let me know if this works for you. I have the exact same issue. I've had instances where the build up in the pan under the bed spilled into the floor hatch while underway. Wasn't sure how to clean it from the top side.
Click to expand...

Your pan shouldn't have a build up, something is clogging the line which is typical in a condensation line that doesn't receive regular cleanings.

The shop vac suction will clear the line without damaging it. Just make sure to do it at the shower sump
 
CaptRonn said:
Your pan shouldn't have a build up, something is clogging the line which is typical in a condensation line that doesn't receive regular cleanings.

The shop vac suction will clear the line without damaging it. Just make sure to do it at the shower sump
Click to expand...
Oh I'm certainly aware that it shouldn't have build up. I just had no idea how to clean it. Thanks very much for the advice of going at it from the sump.
 
THJeff said:
Let me know if this works for you. I have the exact same issue. I've had instances where the build up in the pan under the bed spilled into the floor hatch while underway. Wasn't sure how to clean it from the top side.
Click to expand...
Will do Jeff.
 
THJeff said:
Let me know if this works for you. I have the exact same issue. I've had instances where the build up in the pan under the bed spilled into the floor hatch while underway. Wasn't sure how to clean it from the top side.
Click to expand...
Sorry it took so long to get back to ya. I hooked the ShopVac to the A/C drain line at the shower sump and it definitely seems to be draining better now. Thanks CaptRonn. It still seems to be producing more condensation than the aft A/C but maybe that just has to do with running more or location of unit.
 
Suggest some AC Pan Tablets to keep your system slime free.

Just toss them into the AC pan and they will keep slime from forming in the pan, drain hoses, and sump box.

I toss about 4 into mine once a month.
 
Last edited:
Little Ducky said:
Suggest some AC Pan Tablets to keep your system slime free.

Just toss them into the AC pan and they will keep slime from forming in the pan, drain hoses, and sump box.

I toss about 4 into mine one a month.
Click to expand...
Thanks Ducky, Do you have a brand you like the best?
 
Note that a common misconception about sumps is that they're pumping condensate when cycling often. Condensate doesn't flow that rapidly. The discharge hose is routed uphill to the through-hull and relies on a check valve to keep the water in the hose from flowing back into the sump. Bleach works great to clean a sump. It also is very effective at destroying check valves! My '97 came from the factory with Attwood sumps that had a very fragile rubber (maybe neoprene?) "disk-style" valves. Even regular cleaning products could warp it. I've since upgraded to a more hefty Whale version similar to a duckbill. Even with being careful with cleaners, it's starting to fail now that it's about 5 years old.
 
Sure, but the hotter, more humid the ambient air is, the more likely we are to keep the windows and doors shut, so the interior air gets drier and drier. In a small enclosed space, the inside air becomes more dry every minute that the units are running.

My point is that very often, water flowing up and down the hose is confused for condensate.
 
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