Forum Discussion

JRMunn's avatar
JRMunn
Explorer
Jul 09, 2017

Dometic AC Performance

For background, I am using my father's 2004 Sunnybrook Titan 28RLKS (three pop-outs) 5th wheel trailer after replacing tires and batteries. It was purchased used in about 2009 or 2010 with little use since then because of family health problems, and it shows very little wear inside. There is a single Dometic air conditioner that I assume is the standard option 13,500 BTU unit. I am running it with a Yamaha 3000esi generator, and I can hear (and feel) the compressor working. Air coming out of the roof vents is cool, but not cold, and the AC does not pull temperature from high 80's to high 70's within about an hour. Is this normal? Is there some typical maintenance needed on these AC units? Or does it need to be replaced?

In case it matters, there is an electronic thermostat that has options for AC, heater, and fan which allows setting the start-up temperature but does not show interior temperature. I know the heater works (after filling LP gas tanks), and I am running the AC with fan on AUTO. Much air comes out of the central AC vent, and much smaller amounts of air come out of smaller, circular ceiling vents. The thermostat has a ZONE setting button, but it does not seem to have any effect, so I assume that this is a single zone AC system.

Any suggestions or advice about improving the performance of this AC unit would be greatly appreciated. A big fan helps, but only after we are already hot.
  • darsben1's avatar
    darsben1
    Explorer
    Jul 09, 2017
    Have you climbed on the roof and taken off the cover and checked the coils there, blow out if necessary
    Also has the inside cover been removed and filters checked or filters in the air return which ever you have?
  • kzspree320's avatar
    kzspree320
    Explorer
    Jul 09, 2017
    With one 13.5 AC trying to cool about a 30 foot 5th wheel with 3 slide outs, I would not expect it to go from the high 80s to the high 70s in an hour. If the AC is blowing cold it may or may not have a problem. If I were you I would go to auto supply (got mine at Auto Zone) or harbor fright and get an infrared thermometer (cost about $20 to $30). Shoot the beam to the AC intake and get the temp of the air going into the AC. Then shoot the beam into the main AC output vent and get the temp. If the main AC output vent is about 18 to 20 degrees colder than your input, your AC is working fine. You then need to see what you can do to help the AC. Things such as insulated pads in the roof vents and closing all window shades or even buying foil insulated window coverings. Good luck.
  • JRMunn's avatar
    JRMunn
    Explorer
    Jul 09, 2017
    Thank you for the suggestions! I have been trying to avoid climbing on the roof because I don't know what it will hold or where to step, but will get on top to check coils. I did have the trailer washed at a truck stop, but this was automated. I will also check filters, which looks to be an easy job with a Phillips head screwdriver.

    I wanted to put my best guess/facts in the first post. My impression was that air from AC was just a little cooler than the trailer temperature and there was little, if any, change in temperature over more than an hour. I didn't want to run the AC longer in case it might be damaged by running on low or without refrigerant. I will look into getting an infrared thermometer and will at least have a room thermometer the next time I am able to check the trailer AC.
  • Trackrig's avatar
    Trackrig
    Explorer II
    Jul 09, 2017
    If you can, leave the 3 slide outside in until things have cooled down, then put them out. A single 13.5 is marginal, but it should still put out cold air, not just cool air.

    Bill
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Jul 09, 2017
    Ceiling grill.....
    Has return air section with a foam filter.
    Remove and wash filter, dry and reuse (bag of thin foam filter material at ACE etc....cheap and MANY replacement filters can be cut out)

    With filter removed you can SEE EVAP Coil....and see how dirty
    BUT you have to go on roof..remove shroud and then open sealed cover to access Evap Coil for cleaning (remember that section is OPEN to inside of RV so block with towel when cleaning)

    Also check evap coil drip pan drain holes......free and clear so condensation runs off roof and NOT inside RV

    Under shroud is the condenser coil....it can be sprayed down to clean w/o concern as it is only exposed to outside

    TO check operation...
    Use a 'thermometer' and place it in the 'return air flow' (note return air temp) and then place it in the discharge air flow (note temp)
    S/B 18*F-20*F difference between return air (hot) and discharge sir (cold)

    (Infrared Temp gun not very good at measuring AIR Temps)

    T-stat.
    FAN should be in 'auto'
    Select COOL and turn A/C on EARLY to get jump start.
    Easier to cool down BEFORE inside gets HOT.......heat load from furniture, cabinets etc takes a while to cool off

    Use 'chill grill' to blast air directly down out of ceiling grill for max cooling in local area then swap to ceiling ducts/vents



  • kzspree320's avatar
    kzspree320
    Explorer
    Jul 09, 2017
    Old - Biscuit - agree with everything except what was said about measuring temps. The infrared thermometer works excellent. When you shoot the intake, the ambient air temperature there is almost exactly the same as the plastic around it. If you shoot into the outlet vent and the AC has been running for about an hour or more, the air temp and the inside of the vent (plastic/metal) is about the same temperature. I can regularly get a 20 degree difference when I do this. Plastics and metals change temperature and become the temperature of the ambient air they are in over time. That being said, it is hot in Louisiana and the AC generally runs constantly from about 9AM until dusk. If your AC is cycling and turning off frequently, then it doesn't work as well, since the AC outlet vent will not have fully cooled even if the AC is working. This same infrared thermometer is also very useful for checking tire temps and wheel temps. I wouldn't leave home without one.
  • JRMunn's avatar
    JRMunn
    Explorer
    Jul 09, 2017
    Hello Old-Biscuit,

    Thank you for the detailed instructions. This is good for a novice like me. I really like having the picture of what is inside the housing. Going onto the roof seems necessary, so I am assuming that it will hold me (not too heavy at about 190). One more question - Do these units ever need refrigerant? I have a little experience with car AC units that often need some recharging.

    I have found your other posts to be very direct and helpful. I see you are pulling with a 2007 Dodge 5.9L 3500. I am using a 2008 Dodge 6.7L 2500 4WD. It pulls great, but is marginal on size for the trailer. My father was a true RVer who Started with campers in the 1970's and then travelled all over the country with a 5th wheel trailer. He told me that the 2500 setup with the heavy duty auto transmission and towing package was fine, but he also got used to several earlier model pickups where more was advertised from lesser trucks. Now, the reasons for his opinions are not as clear. And he found that the 5.9 Cummins diesel had plenty of power and got better mileage than the 6.7. I find the travel trailer pulls better than some of the ag trailers I am more used to, but then there aren't large animals moving around in it. Still, I am cautious about quick moves and going downhill. This started out to say that I like the Dodge and hope yours is trouble free. Thank you again for the AC instructions.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Jul 09, 2017
    One hour is simply not enough run time. Air conditioning works best if the RV is never allowed to heat inside.
  • BarneyS's avatar
    BarneyS
    Explorer III
    Jul 09, 2017
    I have the same year Sunnybrook Titan trailer as you do, except that mine is a travel trailer and not a 5th wheel.
    The Sunnybrook Titans all had walk on roofs and you can get up there (carefully of course) and do what needs doing. I, until lately, have been on my roof many times for cleaning, maintenance, and even air conditioner work. I am not a small person but the roof had no problems holding my weight.

    It has been an excellent trailer for all these years and still gives us much enjoyment and pleasure. The Titan was Sunnybooks top of the line unit and was built much better than many of the trailers being built today. I go to the RV shows every year but have never found anything lately that comes up to the quality of the Sunnybrook.

    I just replaced my Dometic 15000 btu unit two years ago because the fan motor required my getting on the roof every time the air conditioner was started after a period of non use to turn it and free it up. Looked like a somewhat major job to replace the motor so I replaced it with an Atwood "Air Command" 15000btu unit with a heat pump. I have been very pleased with the performance of the new unit.

    Enjoy your Sunnybook. Take care of it and it will give you many more years of comfortable service. :)
    Barney

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