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Old 06-26-2011, 01:15 AM   #43
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Originally Posted by Rbphoto View Post
Our new 27FB A/C will only cool to 8-9 degrees below outside air temp. Parked in Lake Powell for 4 days temp at 95. Parked at Lake Havasu temp at 98.....not what the salesman promised of 18 degrees cooling. Cant keep the Zipdee awnings awning out due to the wind. Plan on getting the unit checked out in Denver (where there is only 1 service tech for AS) We also have a fan inside running.
There is a lot of confusion and mis-information about the cooling capacities of RV roof air conditioners. Here is what the manufacturers say about the performance specifications for their roof A/C units: A properly working unit will have a 'delta T' (temperature differential) of 18*F to 22*F measured between the cooled air exiting the ducts or air distribution box (ADB) and the return air measured at the return air grill (usually where the filter(s) are).

THIS MEANS THAT THE COOLED AIR EXITING THE UNIT SHOULD BE 18*F-22*F COOLER THAT THE AMBIENT AIR BEING DRAWN BACK INTO THE UNIT INSIDE THE RV.

THIS HAS NOTHING TO DO WITH THE OUTSIDE AIR TEMPERATURES!!!

It is simply a drop in the INTERIOR air temperature from intake air to cooled exhaust air INSIDE THE TRAILER and again has nothing to do with the outside air temperatures.

If you have been told anything other than the above statement by anyone they are spreading mis-information that is not fact!!!!
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Old 06-26-2011, 09:50 AM   #44
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A recent hot weather camp out in our 27FB gave me the chance to play with many of the suggestions contained in this thread. Our A/C unit is a 13.5 K unit with the old air distribution box, not the one with the quick cool grill.

We were able to leave all three awning deployed. We had OK afternoon shade on parts of the trailer but had lots of morning sun and that hurt us greatly. Two fans were used all day and most of the night. We bought a small Honeywell 10" fan for the front bedroom, placed it on the bed or floor and forced air back towards the A/C unit. The second fan was a fantastic fan stand alone 12V unit placed on the back table during the day or hanging above from the TV antenna handle at night. I had neglected to bring my reflectix foil that was cut for the windows. The would have helped a little in the morning as the rear panoramic windows picked up a LOT of sun. The rest of the windows were covered by shade from the awnings.

I found the air movement helped us feel more comfortable and aided initial cool down but did little for us in the heat of the afternoon. The first day was fine and we maintained an estimated 80 degree average. However day two say outside temps near 102 and interior temps pushed up towards 87. The fans probably helped keep the temps more even, but did nothing to reduce temps in our trailer.

Our site specific problem came from two likely sources: poor site shade and sun orientation and low park voltage. Using our 30 amp service, we were barely able to get 112V with the compressor on. We shed as much load as much load as we could by turning OFF the battery charger (store switch off) and by switching the fridge to LP source during the height of the day. While I have no direct evidence of this, I suspect that the compressor does not work at peak efficiency with low voltages and thus increased resistance and operating temps of the motor and compressor. Maybe Lew could shed some light on this.

While I didn't measure outlet temps on the trip, hot day measurement did show a delta t of about 22 degrees. 92 degrees interior temp was 68 degrees of outlet temp at the rear facing vent. I simply used a small chefs thermometer inserted in the airflow to check. I know the AC is working well under ideal voltages. Simply, the design and poor airflow of the domestic air distribution box limits how well the air mixes with the rest of the trailer air and the restriction it places on the outlet air increases the noise for the blower unit. The placement of the thermostat in the front bedroom makes closing off the front area less than ideal as the unit will just run longer. Of course, it's not like that matters, the AC runs all day anyway.

Lew, any comments on my observations as they relate to the dometic unit?
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Old 06-26-2011, 05:57 PM   #45
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Has anyone ever had, or heard of a problem with the Dometic 15k units? My 2011 27FB AC/HP unit worked fine at the dealer when I picked the trailer up but promptly quit after that. Fan runs, compressor is hot but none of the lines in or out are either hot or cold. Any suggestions?
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Old 06-26-2011, 07:05 PM   #46
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Lewster, thanks for the link to the sunshades.

Long established wisdom for HOMES is that anything that blocks sunlight from the outside is 70% more efficient than anything used inside a window. Awnings, solar screens, trees that leaf out in the summer are simple examples.

I had an attic bedroom with a south facing window. One summer I set out a window box with morning glories and stakes leading to the top of the window. It DID make a noticable difference!

So if you have the windows that open fully, put the prodex or whatever on the outside of the windows. I have the 25 FB, and during the summer I wish I didn't have that wretched skylight (heat sink!). Today I took the truck's sunglasses and put them over the big dining room windows after sewing on two fabric tabs to loop over the top of the window and one to anchor on the bottom. Worked well.

....My next invention will be a big solar "shower cap" for the skylight!
Maybe I should make it look like a blue beret!

I saw an older unit with no a/c where the owner made functional window awnings by draping ordinary towels over the top of his windows, and used a "U" shaped piece of aluminum tubing (looked like a cut up lawn chair with corks on the ends) to hold the awning away from the window. He'd actually safety pinned the towels around the U-shaped awning bar. Quick, cheap, and multipurpose.

Paula
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Old 06-26-2011, 07:50 PM   #47
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Homemade and even works!!

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Long established wisdom for HOMES is that anything that blocks sunlight from the outside is 70% more efficient than anything used inside a window. Awnings, solar screens, trees that leaf out in the summer are simple examples.
Being a temporary Texas resident, I have had to improvise because I am not rich and I like coolness...I have dropped the temperature in our trailer by at least 15 degrees when it is 100 or above outside. We placed a large truck sun screen in the front window and it still felt like we could bake chicken on the outside of the front curtains. So I did the following:

Purchased a 25 foot by 4 feet roll of bubble-type insulation for $42. Bought one roll of duct tape and trimmed a piece of insulation for each window in the trailer. I then placed a long piece of duct tape on three sides (not on the hinge side) of the pre-cut insulation with about 1/3 on the insulation and 2/3 over the edge. I turned the insulation over and placed another matching piece of tape sticky side to sticky side of the matching tape covering 1/3 of the width of the tape on the insulation. I then opened the window and placed the insulation on the outside of the window. I closed the window onto the non-sticky duct tape border and it is held firmly between the rubber seal and the window frame.

Here are some pictures of my finished product...
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Old 06-26-2011, 08:57 PM   #48
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foil backed panels

We used several foil backed window deflectors, cut to size to shield all overhead fan/vent and skylight openings. Also cut several for the round windows in the front and full rear window. Along with opening the awnings, this addition made a HUGE difference in comfort during extreme temps.
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Old 06-26-2011, 09:16 PM   #49
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The only thing I miss about the old SOB. It cooled much better in very hot weather... These Airstreams are just ovens!
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Old 06-26-2011, 09:32 PM   #50
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We have never summered in the heat down South. I was hoping to hear that the Classic hull and head liner materials would help insulate. Our 04 doesn't have any skylights or vista views. We have used the foiled bubblewrap (Reflectix) in the sunny windows between the closed shade and windows and in the Fantastic Vents for a visit in Florida and that seemed to help. We have the 12 volt Endless Breeze which is quiet light and moves a lot of air and makes the heat more bearable. We used the fan in leu of AC when we were in 3 amp during a heat wave at an International Rally. One can definitely feel a good 10 degree plus difference between the insulated and bare aluminum units from my experience while popping in and out of other Airstreams. It was a noticable difference, but I did compare temperatures as well.
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Old 06-27-2011, 10:22 AM   #51
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Emerson Fan

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We have never summered in the heat down South. I was hoping to hear that the Classic hull and head liner materials would help insulate. Our 04 doesn't have any skylights or vista views. We have used the foiled bubblewrap (Reflectix) in the sunny windows between the closed shade and windows and in the Fantastic Vents for a visit in Florida and that seemed to help. We have the 12 volt Endless Breeze which is quiet light and moves a lot of air and makes the heat more bearable. We used the fan in leu of AC when we were in 3 amp during a heat wave at an International Rally. One can definitely feel a good 10 degree plus difference between the insulated and bare aluminum units from my experience while popping in and out of other Airstreams. It was a noticable difference, but I did compare temperatures as well.

We use a 1929 Emerson Brass blade fan. Fans make a big difference.
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Old 06-28-2011, 12:29 AM   #52
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Has anyone ever had, or heard of a problem with the Dometic 15k units? My 2011 27FB AC/HP unit worked fine at the dealer when I picked the trailer up but promptly quit after that. Fan runs, compressor is hot but none of the lines in or out are either hot or cold. Any suggestions?
DMT,

Sounds like your unit has lost the refrigerant due to a leak. If the fan and compressor are working but you are not getting any heating/cooling, then there probably is no refrigerant left in the unit.

The best way to tell is to have an amp draw test doe on the main compressor lead. If the unit is not drawing close to what the data plate specifies (this must be temperature corrected) then you might be in line for a new unit. These new units are hermetically sealed at the factory and have NO process valve on them like residential units, so they can't be re-charged.

Good luck!
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Old 07-03-2011, 10:29 AM   #53
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Thanks. Sounds like that may be it as I'm running on two Honda 2000i's in parallel and they do not bear down much when the compressor starts. It worked fine at Colonial in New Jersey but maybe something came loose during the tow back to Canada.

We're on the fifth day of the maiden voyage and other than the AC all I have managed to break is the screen door latch. Don't know why they made it out of cheap plastic. My wife has it held closed with twist ties which are working pretty good? Go figure.

Trailer is great though. Tows like a dream and really comfortable to stay in. Can't get the smiles off my kid's faces!
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Old 07-03-2011, 01:20 PM   #54
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Will 2 2000 in parallel run a 15k unit? jim
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Old 07-04-2011, 05:47 AM   #55
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Will 2 2000 in parallel run a 15k unit? jim
Yes. The econo mode has to be turned off on both to ensure the gens can throttle up fast enough.
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Old 07-04-2011, 08:46 AM   #56
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I had a Dometic 13.5 that wasn't cooling very well and found that the evaporator box inside the unit on the roof was not snapped together and was pulling outside air. Even after snapping it back together it wasn't a tight seal so I ran in a half dozen #10 sheet metal screws to secure it. It made quite a difference from before. Easy to check, just pull off the big cover and its the black plastic box in front.
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