A/C Water Dripping On Bed - PROBLEM SOLVED

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A/C Water Dripping On Bed - PROBLEM SOLVED

June 23, 2015, 10:29:46 am

On our recent trip to NAC in hot, humid and rainy conditions, I reported a problem with water dripping out of the rear A/C vent onto our bed. The front A/C was still working perfectly under the same conditions. I first tried the easy stuff, like running the fan on "HIGH" rather than "AUTO", and tilting the coach in different directions. Did not help.

I then went up on the roof, and observed that at the front A/C unit condensate was draining normally out of the drain holes onto the roof, while at the rear A/C there was ZERO water coming out of the drain holes. I removed the white shroud on the rear unit, thus exposing the innards of the unit. I observed water (condensate) pooled in several places in the gray metal bottom pan, which is NOT where water should be found. Running the unit with the shroud off, I could actually see the water level in the pan increase, but could not see where it was coming from. I was running out of daylight, so I quickly removed the sheet metal cover over the evaporator. I inspected the drain holes on both sides of the unit, and they were completely open! Puzzled and with no explanation for the errant water flow, I put the unit back together and we completed our trip running on only the front A/C.

Back home with the coach in our driveway, I again tackled the problem. Tried searching Google for answers. If you seek help online with roof mounted RV A/C problems, you will encounter 2 standard solutions.

First, you are advised to check and tighten (if necessary) the mounting bolts that hold the unit on the roof. There is a 14" square black rubber gasket that fits between the A/C unit and the roof. This gasket seals the opening in the roof, and keeps water on the roof (which might be rain water, condensate draining out of the unit, etc) from entering the coach at that point. If the mounting bolts are loose, it is possible for this gasket to leak. I checked the bolts on our units, and indeed found all of them needed some tightening - a couple were barely "finger tight". So, checking these bolts IS good advice, but it did not solve my problem.

Second, you are advised to "clean the evaporator coils, and check to see if the drain holes are open". This step actually lead to my discovery of the cause of my problem. I again removed the white shroud with the unit running. Again, there was no water coming out of the drain holes, but water was pooled in the gray metal pan. Shutting down the unit, I then removed the metal cover over the evaporator. Unfortunately, I did not take any photos of this operation, but I will explain as best I can the design of the Dometic DuoTherm Penguin. With the metal cover removed, you see the evaporator in all it's glory. Mine is very clean - the PO's must have been diligent about cleaning the filters.

The evaporator gets extremely cold when the A/C is running, and IT is what produces the condensation that you normally see running off your roof. Under and around the evaporator, there is a molded white styrofoam structure. Why the designers used that particular material, I don't know...perhaps for its insulating value. The part of this structure directly beneath the evaporator incorporates a drainage channel which leads to the drain holes on each side of the A/C unit. The condensate is supposed to run off the evaporator, drip onto the styrofoam, and then follow the channel to the drain hole on one side or the other (depending on the tilt of the coach). Even though the drain holes were both open, and the channel also appeared to be clear, I could see some dark dirt/mold under the evaporator and in the channel. It is almost impossible to reach this area unless you move the evaporator, which I then did. If you remove the two mounting screws, it is possible to CAREFULLY raise the evaporator up about 2 inches without damaging the connected hard tubing lines. Now able to access the drainage channel, I gently cleaned out the muck and dirt with paper towels and Q-Tips. With the bottom of the drainage channel clean and fully exposed, I FOUND MY PROBLEM!

The bottom of the drainage channel appeared to be deteriorated along its entire length, and there were several HOLES in it. I could see the gray metal pan through these holes! Finally, I understood what was happening. The condensate from the evaporator was following the drain channel until it encountered a hole, then it was running out the hole into the gray metal pan below. Once in the pan, it would pool in the low spots until it reached some screw hole or other opening, ALL of which lead to the interior air distribution portion of the unit. From there it would drip on the bed. That was why I did not see water coming out the normal drain holes onto the roof - it never made it that far.

The solution was simple: fill the holes. I used a general purpose white water-proof sealer, and spread it smoothly on the bottom of the drain channel with a small screw driver blade. A even better solution would be some type of "self leveling" sealer, like Dicor or a thin epoxy. But I used what I had on hand. Put everything back together, and let the repair dry overnight. Next day, fired up the A/C for a test. After a short while, the water starting running out the drain holes! I let it operate all day and it functioned perfectly. Water was running off the roof in a small waterfall, and inside the coach everything was totally dry. SUCCESS!

My only question now is "What caused the holes?" Chemical decomposition of the styrofoam, vibration, plastic-eating mold.......? I don't know. I will definitely be checking the condition of the front A/C unit at the next opportunity. Now that I know what to look for, it will be a simple matter to repair any damage I find, BEFORE it causes a problem. I hope this (long) post will help other Forum members with dripping A/C units.

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #1 – June 23, 2015, 01:20:53 pm

Chuck, great post!

Excellent deduction of a leaking problem that could be there on a lot of these older A/C units. I have the same same Dometic Penguins and now have another low tech DIY solution to try if they start leaking inside. My front unit dripped inside some last week while I had them on and was working other things. It's probably a good idea to do what you did as part of the preventative maintenance and inspection/cleaning. I'm sure you saved me and other members here quite a few $$$ by doing it yourself and showing us How To!

Jerry

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #2 – June 23, 2015, 01:34:52 pm

Thanks for your detailed posting. Ours drips periodically (front unit) and I've yet to be able to find the reason. However, ours is a 2012 unit, so deterioration shouldn't be the problem. I'll be up on the roof examining everything you described. Congratulations on your success!

Chris

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #3 – June 23, 2015, 02:30:10 pm

One thing I will add is do not over-tighten the hold down bolts. They should be at the manufacturers correct torque setting. This is important as over-tightening will compress the gasket and lead to the unit becoming louder and the compressor vibrations introduced into the roof structure causing a droning sound.

Keith

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #4 – June 23, 2015, 05:21:50 pm

Quote from: Keith and Joyce – June 23, 2015, 02:30:10 pm

One thing I will add is do not over-tighten the hold down bolts.

Good advice! The manual for the Penguin calls for 40-50 INCH pounds. The gasket should be compressed evenly all the way around, and to "not more than 1/2 original thickness". Of course, that last bit is difficult to judge unless you were the one who installed the gasket. For what it's worth, both our units sounded quieter and there was less vibration after I snugged down the bolts.

http://www.bdub.net/manuals/DuoTherm_Penguin_610115_Install-Operation.pdf

I also took the opportunity, since I had to R & R the shrouds multiple times, to upgrade the fasteners. Our shrouds are of unknown age but are in excellent condition. There are no cracks around any of the mounting holes, and I would like to keep it that way. There were 4 TINY little sheet metal screws holding down each cover! No wonder those things blow off. There are 4 additional mounting points (which are not being used) for the shroud pre-drilled in the metal pan. I drilled holes in the shroud for the 4 additional screws, and ended up with 8 up-sized bolts and washers holding down each shroud. Seems much more secure to me.

Photos: Old fastener (the little one), and new fastener + stainless washer:

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #5 – June 23, 2015, 05:50:48 pm

Thanks Chuck, get information and great write up.

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #6 – June 23, 2015, 08:36:12 pm

Were you a Technical writter in a past enployment ?
I give you an "A+" for your write-up's, and an "A" for your technical ability

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #7 – June 23, 2015, 09:15:09 pm

Quote from: Bill Chaplin – June 23, 2015, 08:36:12 pm

Were you a Technical writter in a past employment ?

No, but I was a English major (although I barely made it through school).

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #8 – June 24, 2015, 11:56:14 pm

Quote from: Andy 2 – June 23, 2015, 05:50:48 pm

Thanks Chuck, get information and great write up.

Yes,
Great, detailed write up.

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #9 – June 25, 2015, 09:31:48 am

It is a good idea to use stainless steel screws and washers for all those shroud screws.
Good write up.

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #10 – October 12, 2015, 09:27:44 pm

Wow! Great responses from you all, especially you, Chuck.

Too hot to go up on the roof for a while, but it leaked inside again today after the cycle with the fan on high, though not as much. Oddly. it did not leak outside the coach. Geez, just when my clipboard was getting empty of projects: it never ends, does it? M (I just noticed I was on the wrong thread. Oh well, it's all AC!)

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #11 – October 12, 2015, 09:58:20 pm

I have this issue with my rear A/C too. Was up on the roof with my Repair guy and he was baffled as to how the water was getting in and dripping on the bed. The inside of the unit looked perfect even after 22 years... I will fix it myself and save some $!!

Thank you!

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #12 – October 12, 2015, 10:19:55 pm

Thanks for the diagnose, I had my rear ac was leaking this summer but never found out why and it never happened again so I had
forgotten ed about it until now. If it happens again I will do as you suggested. With Styrofoam you need to be careful in what you
use as a lot of fillers eat Styrofoam. I will use Styrofoam wallboard glue.

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #13 – October 13, 2015, 08:36:04 am

Our original (1989) Dometic AC over the bed leaked, even when not on, but also whenever it rained. Turned out the rear bolt on the driver's side that held the shroud on let water run inside thru the bolthole. The water then ran down the copper tubing into the interior of the coach. Each hold down bolt is in a recess so when it rained the water collected in the recesses. I put a fender washer under each bolt and some caulk over the top. Haven't had any water inside since.

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A/C Water Dripping On Bed - PROBLEM SOLVED

June 23, 2015, 10:29:46 am

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #1 – June 23, 2015, 01:20:53 pm

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #2 – June 23, 2015, 01:34:52 pm

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #3 – June 23, 2015, 02:30:10 pm

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #4 – June 23, 2015, 05:21:50 pm

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #5 – June 23, 2015, 05:50:48 pm

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #6 – June 23, 2015, 08:36:12 pm

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #7 – June 23, 2015, 09:15:09 pm

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #8 – June 24, 2015, 11:56:14 pm

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #9 – June 25, 2015, 09:31:48 am

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #10 – October 12, 2015, 09:27:44 pm

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #11 – October 12, 2015, 09:58:20 pm

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #12 – October 12, 2015, 10:19:55 pm

Re: A/C Water Dripping On Bed - PROBLEM SOLVED

Reply #13 – October 13, 2015, 08:36:04 am

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