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Old 06-26-2016, 07:46 PM   #1
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AC drainage question

So here's the deal. My ACs do not drain while the fan is on. Apparently the air flow causes some sort of vacuum or resistance that prevents proper drainage. So while the fan is on, water accumulates in the pan. When the fan shuts off, the pan drains beautifully.

So, if the fans are set to AUTO, they turn off every once in a while (when the desired temperature is reached) and the pans drain fine. But, if I leave the fan on HI, after a couple of hours the pan fills up and the ACs start to leak inside the Airstream.

Sigh.

Florida weather is particularly hot and humid this time of year, but I'd prefer to set both ACs to HI all the time. Any chance this drainage quirk can be remedied?
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Old 07-03-2016, 12:39 AM   #2
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You need a trap in the drain. The water level difference in the trap will counteract the negative pressure caused by the fan.
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Old 07-03-2016, 12:41 AM   #3
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PS: make sure the trap can be cleaned, and do so regularly!
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Old 07-06-2016, 08:55 AM   #4
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I'm sorry, I don't understand the term "trap". Excuse the noobie. What does that mean?
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Old 07-06-2016, 11:36 AM   #5
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Quote:
Originally Posted by FCStreamer View Post
I'm sorry, I don't understand the term "trap". Excuse the noobie. What does that mean?
No problem. Google "condensate trap detail" for a better explanation than I could give you in writing. Note that the trap can also be at the bottom end of the tube, just as long as you leave yourself a way to clean it out.
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Old 07-07-2016, 02:46 PM   #6
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I don't see how a trap is going to help. The OP is still going to have a vacuum, keeping the water from draining. There may be an airflow restriction somewhere, causing the vacuum.

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Old 07-07-2016, 03:52 PM   #7
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Apparently, this is a common problem. I started the thread below a few weeks back (no solution though).

The condensate trap discussed above is common in household AC systems, but my trailer never had a trap, and I have never heard of having a condensate trap in a trailer. Should be unnecessary as the condensate tube just drips onto the ground. The main purpose of a trap in a household system is that the condensate is usually plumbed into the household waste plumbing and you would want a barrier between your air circulating system and whatever funk may be in the pipes.

http://www.airforums.com/forums/f427...ng-152630.html
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Old 07-07-2016, 04:31 PM   #8
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Another drawback to the trap in the RV system is that it may freeze up and crack drain tubing. Then you have the problem of leakage, etc. I am on the "No trap" side of this AC thread.

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Old 07-07-2016, 06:25 PM   #9
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Ok, no trap. How do I relieve the vacuum or pressure that is causing my drains to fail?
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Old 07-07-2016, 06:37 PM   #10
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The "vacuum" concept it seems to me is misplaced. Unless your units are ducted and programmed to vent interior air to the exterior, they do not create a vacuum inside the trailer IMO. Maybe the newer units like yours have a function like this?

If not, there is another cause for the leaking, and other threads have mentioned the drain tubing being crimped inside the ceiling or walls from shoddy craftsmanship during assembly. Nothing new to mention this . . . Sorry to say.

I am on the road now, but check out Posts 918 to 950 in the following 20-footer thread for another possibility -- a missing hose clamp on the condensate discharge tubing. See also the threads from which the quotes come.

http://www.airforums.com/forums/f516...rs-127845.html

I will look into this more over the weekend.

Good luck!

Peter
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Old 07-07-2016, 07:32 PM   #11
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What troubles me is that the unit drains fine when the AC fan is off. This tells me it's not the drain lines. If something was crimped somewhere, it wouldn't drain at all. The fact that it happens with the fans on leads me to believe there is some sort of pressure caused by the airflow that is interfering with the drain flow.

I of course am not an engineer, but I did stay at a Holiday Inn Express...
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Old 07-07-2016, 07:51 PM   #12
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Without looking at the exact setup it's hard to say.
It seems like the drain pan is open to the suction side of the air flow. This means the same low pressure pulling air up into the ac is also keeping the water from draining. A strip of foam insulation between the bottom of the evaporator coils and top of the drain pan may be able to block the negative pressure enough.
Do you have the drain cups?
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Old 07-07-2016, 07:53 PM   #13
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Quote:
Originally Posted by HiJoeSilver View Post
Do you have the drain cups?
Don't know what those are so I'm going to go with "no".
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Old 07-07-2016, 11:18 PM   #14
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Even though nobody understands the trap concept, it's exactly what's needed here. The suction that's keeping the condensate in the pan will be compensated for by the difference in liquid levels in the trap. That's what traps are for.

I am, seriously, a Registered Professional Mechanical Engineer with extensive training and experience in HVAC.

Try making a very simple trap, maybe six inches deep or so, with just a plastic barb fitting on the end to connect to your drain line. It will work and it will solve your problem.

Then you can work some more on making it durable, cleanable and removaable for winterizing.

Here's your homework: http://diy.stackexchange.com/questio...aining-problem
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