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Old 07-08-2016, 11:35 PM   #29
2 Rivet Member
1976 Argosy 26
diamond bar , California
Join Date: Feb 2016
Posts: 94
Originally Posted by Belegedhel View Post
Well, based on the fact that these trailers seem to have never been built with a trap, and this drainage problem seems to be so common, there may very well be a cause and effect relationship here.

So, it seems like this should be pretty easy to test. If a guy were to simply plug the end of his condensate tube and then run his AC for a while, and then unplug the condensate tube, a column of water should come gushing out, right? Maybe I'll try it this weekend. Maybe a check valve is all that is needed--something that resists the air suction, but lets the water drain.

Another thing I will try is removing my filters to see if I get a different result in the as-is state. As several others have noted, my trailer didn't always drain like this, so something has changed--could very well be a clogged air filter that is causing more of an air-pull up through the condensate tube.
I do not know a thing about RV AC but if you have filters, this is the first place I would look. A restrictive/clogged filter will create more suction with in the unit, which will prevent the water from draining.

My 2 cents on what the trap is prevent outside air, near outlet of the condensate drain to be pulled into the unit. Not the other way around.

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Old 07-09-2016, 06:04 PM   #30
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1973 21' Globetrotter
Houston , Texas
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Allright, I have been doing some experimentation today. I have a plain-Jane Dometic low profile 13500 unit with no house thermostat and no ducting besides the vents built into the ceiling unit. The AC sits in one of those plastic condensate capture pans that the factory used to use.

First I ran the AC for a while to ensure that it was still having the drainage issue. No drippage from the condensate tube until I turned off the AC, then it streamed out.

Next step, I plugged the end of the condensate tube. This should reproduce the effect of having a trap at the end of the tube. I unplugged the end of the tube (with AC still running) after a similar amount of time to the first step above, but no water came gushing out. Turned off the AC, and again, I got a stream of drainage. So no apparent improvement.

Next, I ran the unit with the trailer level, slighty nose up, and slightly nose down. No improvement, or even change from posistion to position.

Next, I removed my ceiling unit so that I could see what is going on. One thing for sure, the filters were slightly dirty, and the AC was really deforming them as it sucked on them. Removed all of that and ran it "commando" for a while. Now I sterted to get a little drippage at the end of the drain tube, so maybe the combination of filters and ceiling shroud are contributing to the problem. Next thing I noticed with the ceiling unit out of the way, was that I started getting water dripping out of the AC from inside the intake vents. Looked up in there, and could see that there was moisture condensing on the plastic cowling/body of the AC that channels the intake air into the heat exchanger/ ("radiator"). So, here I have a new problem (or a pproblem I have seen before, but didn't realize the cause of it)--drippage that has nothing to do with the condensate handling system.

So yes, it is hot and humid as all heck here in Houston, so maybe the humidity exceeds the capability of the design of the AC to deal with it. The drainage issue still seems to be more of a problem of airflow "pushing" the condensate away from the drip holes in the unit--will have to lift the shroud as the next step.

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Old 07-10-2016, 01:45 AM   #31
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1976 Argosy 26
diamond bar , California
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Props to you on tackling the troubleshooting head on.

The fan needs to pull air in any where it can. As the filter or restriction gets worse, the fan will try and pull air in from any where it can, including the condensate drain line.

Another item to check is that pan you are talking about. Make sure it is sloping to the drain hole. Not really sure what it looks like though.
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Old 07-11-2016, 02:12 PM   #32
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1973 21' Globetrotter
Houston , Texas
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I spent the better part of Sunday doing further troubleshooting. Took the shroud off expecting to see something interesting, but discoveries were minimal. One thing for sure, though is that on both the curb and street sides of the AC unit there are electrical lines or coolant lines that penetrate from the outside to the interior of the unit (they come into the AC in the interior intake area). What I discovered is that where these penetrations occur, the hole is gooped up with some kind of butyl material that not only stays flexible, but has sagged over time (three years, maybe), to allow outside air to be sucked into the intake side of the AC. I am guessing that this is where the moist air was coming from that was creating the condensation inside my unit, as mentioned in my previous post.

I posted several pictures below. I circled the sagging butyl in a couple of the pictures. On one of them, I had already massaged the goo back into place before taking the picture, the "street side" pic shows the sag pre-repair. I also noticed that I was getting some condensation on the top of the plastic intake area. I suppose if left long enough, this could result in the condensation running down the outside of the trailer that I have noticed in the recent past. I wonder if I should put a layer of insulation on there to help keep it from sweating.

Also pretty sweaty was the cold coolant line that leaves the compressor and goes to the evaporator coil. I was surprised that this line doesn't have any pipe wrap on it. Incidentally, the cold lines in my VW's AC system are similarly uninsulated...wonder if the reason is just added cost, or if there is a better rationale.

So I put my shroud back one and ran the AC for a while again. I found that without the interior ceiling unit in place, and the fan at about half speed the condensate would drip-drip-drip out of the tube as expected. If I turned it up to full blast, the dripping would stop again. I am no longer getting the condensate forming on the surfaces of the intake side in the interior, so I would conclude that the butyl sag mentioned above was responsible for humid air getting into my system.

I made certain that my condensate drain tube is clear (it was clear in the first place, just confirmed it). Looking at the little "plumbing" from the outside where the condensate is caught and then channeled to where it would just drip out on the roof, if the catch-pan wasn't there, I am still confused as to what is happening.

My next step will be to completely remove the celing mounting hardware so that I can see all along where the AC unit sits in the condensate drain pan. I didn't seal the two together, so maybe air is being drawn across a crack in this interface and causing some kind of suction or something. I figure I can tape it up with aluminum tape and see if that improves things.
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Old 07-11-2016, 03:47 PM   #33
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1965 26' Overlander
Tulsa , Oklahoma
Join Date: May 2006
Posts: 362
Nice work! I'm curious if that's way occasionally mine drips inside on humid days? I have a 3 year old dometic 13500 on my 65 Overlander w/ no drain line. I'm going to pull cowl off to investigate!

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