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FCStreamer · 06-26-2016, 06:46 PM

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?

drboyd · 07-02-2016, 11:39 PM

You need a trap in the drain. The water level difference in the trap will counteract the negative pressure caused by the fan.

drboyd · 07-02-2016, 11:41 PM

PS: make sure the trap can be cleaned, and do so regularly!

FCStreamer · 07-06-2016, 07:55 AM

I'm sorry, I don't understand the term "trap". Excuse the noobie. What does that mean?

drboyd · 07-06-2016, 10:36 AM

Quote:

Originally Posted by FCStreamer

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.

AstroBruce · 07-07-2016, 01:46 PM

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.

Bruce

Belegedhel · 07-07-2016, 02:52 PM

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

Farmer Dan · 07-07-2016, 03:31 PM

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.

Dan

FCStreamer · 07-07-2016, 05:25 PM

Ok, no trap. How do I relieve the vacuum or pressure that is causing my drains to fail?

OTRA15 · 07-07-2016, 05:37 PM

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

FCStreamer · 07-07-2016, 06:32 PM

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...

HiJoeSilver · 07-07-2016, 06:51 PM

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?

FCStreamer · 07-07-2016, 06:53 PM

Quote:

Originally Posted by HiJoeSilver

Do you have the drain cups?

Don't know what those are so I'm going to go with "no".

drboyd · 07-07-2016, 10:18 PM

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

OTRA15 · 07-08-2016, 04:15 AM

Quote:

Originally Posted by FCStreamer

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.
. . .

Thanks. OK one step at a time . . .

Do your AC units allow you, like in a car, to toggle between "Recirculating" the interior air, and the alternate of bringing in outside air?

Also these are non-ducted AC units, right, not the new ducted models?

OTRA15 · 07-08-2016, 04:23 AM

A new trap will not prevent air from bubbling back up through the water in the trap, if indeed there is some kind of vacuum being created here.

Also, as mentioned earlier, Airstream trailers do not have such traps and most of the AC systems work fine.

Aside from the difficulty of installing a trap near the unit (and one near the discharge would not do the same job even if a trap might help here IMO), it is simply a Bandaid for a more complex problem, again IMO.

The facts/system in the air handler link are way different, and the volume/height of trap water required to withstand the vacuum makes its applicability to this AS trailer doubtful at best IMO.

OTRA15 · 07-08-2016, 04:42 AM

FCStreamer, one experiment you could try is to raise the trailer tongue to see if the drainage resumes alright. On the 20-footer thread someone said this helped his AC drainage. [or maybe lowering? Can't find that post right now.]

Have you removed your lower shroud on the AC and checked for hose clamps the way I pictured, as linked last night?

centennialman · 07-08-2016, 05:06 AM

Following....I had issues similar to this on the trip this last weekend. When the air would shut off the drain worked fine. When the air was working the water drained off of both sides of the front end cap.

Belegedhel · 07-08-2016, 08:11 AM

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.

drboyd · 07-08-2016, 09:18 AM

Quote:

Originally Posted by OTRA15

A new trap will not prevent air from bubbling back up through the water in the trap, if indeed there is some kind of vacuum being created here.

<snip>

The facts/system in the air handler link are way different, and the volume/height of trap water required to withstand the vacuum makes its applicability to this AS trailer doubtful at best IMO.

In fact, three inches of water column would be a very high pressure for a fan. The purpose of the trap is exactly that - to prevent air from bubbling back through the water and diisrupting the flow. A trap at the bottom of the tube will work just as well and will be more convenient to access, drain, and clean.

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