Today’s Roof Air Conditioner Choices

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June 22, 2008

Air conditioning is something that many of us have come to expect, whether it is in a house, car, office or RV. In many cases it is no longer an option as it once was. That is the case with most, if not all, motor homes and trailers today. While there are also manufacturers that mount the A/C units in the basement, we will only deal today with roof mounted. There are, and may be, configuration choices with options when it comes to ordering a new rig or replacement A/C unit. The selection may include the number of units, output capacity, heat strips, heat pumps, height profile, air ducted and possibly the thermostat control type. While many of these will probably not be a choice when purchasing a new rig, it is possible that a couple may, particularly if you are ordering a factory build. Let’s look at these choices.

Number of Units: Single A/C units are standard on Class “C” and “B” coaches, most trailers and shorter, entry level class “A” coaches. Larger class “A” coaches usually come standard with two units. The largest group of class “A’s”, 42′ to 45′, generally come standard with three A/C units.

In some cases, for those with only one unit, an additional unit can be ordered. This would apply to the class “A”, the trailers and possibly larger “C’s”. The “A” coaches equipped with two units may be able to specify a third A/C. Keep in mind, many of these upgrades may require changes to internal wiring and or, generator size, which may add considerably to the cost.

Output Capacity: There are several sizes, all rated in B.T.U. output, but the most popular being 13500 and 15000. Generally these require about 14.5 amps and 15.7 amps respectively, of AC power to operate. This however, can vary with different manufacturers. As the output is only about 11% difference, it is difficult to differentiate the two inside your coach.

Heat Strips: Are exactly what they sound like, they are heating elements within the A/C unit. Typically these provide about 5600 B.T.U.’s of heat when in use. These are not generally used on ducted A/C installations.

Heat Pumps: Heat pumps do not use heating elements. They basically reverse the A/C cycle exhausting the chilled air outside while warmed air is directed inside. These are very efficient and work well down to about 40 degrees F. outside temperature. Most heat pump set ups in today’s RV’s are wired to automatically switch to another heat source such as a furnace or HydroHot/Auqua Hot when outside temperatures warrant it. Likewise, they will re-start when the temperatures return to above 40 degrees F.

Height Profile: There are two common profiles, standard and low profile. The standard units project 12″ to 13″ above the roof, while the low profile is about 9″ high. Advantages are less wind resistance, can contribute to a lower overall vehicle height, and appearance.

Air Ducted: In most, if not all RV models, this is not a choice as it either comes that way or it does not. This is a good feature that can more evenly distribute the air throughout the coach.

Thermostat Selection: In some cases an optional remote thermostat can be purchased. This can provide the convenience of being able to set and monitor the temperature in any location within the coach. It may also provide a more precise control than that normally installed.

Anyway, that’s a brief simple version of what’s out there. Whether you are ordering a new recreational vehicle or replacing a worn out air conditioner, these are some of the choices and decisions you may have to make.

With More Cool Ideas – Lug_Nut

Leave a Reply


  1. Mark

    I have a 2007 35′ Carriage Cameo with a ducted installation. Originally the air unit was a Carrier AirV 15K unit. It never was able to do a good job of cooling the RV. When it went south, I replaced it with a Dometic 15K A/C. It too doesn’t seem to keep up.

    I understand that these units are supposed to provide a 20-25 degree differential between intake and output.

    Is there an A/C that can handle a 35′ 5er’s living area with a 13500 in the bedroom (this unit workd great)?

  2. good post…………………………………

  3. Lug_Nut

    Greta, Sounds like a drain issue. This water would normally drain outside. It may be best to seek a good RV dealer that can check the problem out. Hopefully a small correction will fix it up. Thanks for your post.

  4. Greta

    We just got a 1997 Gulfstream Friendship 102 with 2 roof top air conditioners. I can’t give the brand right now b/c I can’t climb the ladder to look (that’s a long story). The back unit over the bedroom works great. The front unit works great EXCEPT when the unit automatically shuts down or we turn it off, there is either dripping or a fine stream of water which we are now catching in the kitchen trash can. We’ve replaced the filter. We have manuals for everything but the ACs. Suggestions? Any help will be appreciated.

  5. malisa

    hi im looking for a small aircondioner that will go in the roof of my work cube van i have looked for this for awhile now have no idea what it is called or what to ask for so if anyone knows please email me at [email protected] and if you know where i can buy one of these things please also let me thanks a bunch

  6. Lug_Nut

    Walter Burmylo, There is no place to connect a hose as the evaporator just drips in general. There are units that have a pan that surrounds the AC unit that a hose can be attached to. These may not be ideal though as any movement may cause the water to spill out very easily. Some high end coaches have channeled drians off that leads to drain holes that are tubed down imside and out. Drip rail extensions are also very popular and just take the water a couple of inches from the body. I hope this is of some help to you. Thanks for your post.

  7. Walter Burmylo

    Is there a way to attach a hose to the drain off on my roof top air.I have a Mallard Park Model.With a shingled roof and would like too run the drain off to the rear of the camper.If you have any suggestions it would really help.thank you

  8. Lug_Nut

    Mini Split Air Conditioner, Glad you got something out of the article. Thanks for posting.

  9. Mini Split Air Conditioner

    Thanks for information. RVs are getting more sophisticated everyday.

  10. Rusty Basinger, There are different size A/C units available, each requiring slightly different current loads. Generally you need a generator large enough to handle not only the rated wattage of the A/C unit, but also to handle the compressor start up load as well as some additional capacity for your charger and like equipment. This will pretty well mean you will probably need a 3000 watt for a smaller single unit and up from there. I hope this is of some help. Thank you for your input.

  11. Rusty Basinger

    What size generator would i need for ac units

  12. Jim

    More than likely the problem with your A/C freezing up and resticting the air flow across the evaporator coil, is that the switch that controls the compressor is either faulty or not properly installed. This is a sealed switch that senses the temperature of the evaporator coil which in turn turns the compressor off and on. Remove the inlet air filter and shine a light on the evaporator coil to see if you can see the switch (about the size of a quarter and 3/4″ thick) that is attached to the coil fin or U bend tube. If the switch is hanging loose, take the unit to a RV repair shop so that the top cover and sheet metal duct work can be removed to gain access to the evaporator coil. Since I work on A/C units, this is probably the source of your problem. Sounds like the individual that installed the 15,000 btu unit did not reinstall the compressor temp. control switch. This switch is part of the controls that in mounted directly above the inlet air filter and would not necessairly have been repurchased with the larger A/C unit. But the switch that I have described has to be connected to the new larger units evaporator coil.
    The 15,000 Btu A/C unit has sufficient capacity if properly working to cool your trailer in 100+ outside temp.
    I know that this is a long winded answer or comment, but that is how we southern boys are.

  13. Tracie, If your air conditioner froze it may be an indication that it is too large for the space/air flow. It’s kind of like your house. If it requires a 1 – 1/2 ton A/C unit and you put a 3 ton unit in it will freeze up and not allow air flow. Check your air flow and try to increase the air circulation to stop it from intaking cool air.

  14. Tracie

    Have a Komfort 25ft travel trailer and I go visit my son every summer and work in an rv resort for a month in quite hot weather.
    Couple of years ago, we removed the AC (13,500 btu) that came with the trailer and installed a 15000 btu. In the hot weather (95-103), inside the trailer still gets warm and throught the day it gets hotter.
    Last year I really started to notice that it would get too warm inside so something appeared to be “frozen”. Not sure if that is the correct word or not. If I shut off the AC for about 15mintues or so, then there would be water again dripping down the outside and the inside would start to cool again.
    1. Is this normal?
    2. How come they do not make anything above 15000 btu?



  15. larry marshall

    Can anyone tell me which Coleman RV airconditioner will start and run with my 2000 Honda generator. I’m considereing either the Polar Cub or the Mark 3 P.S. I have a 8 1/2 foot camper and boondock a lot in the summer. Thanks for reading this.

  16. Maxine Simon

    Hi I have a big concern and can not get a straight answer. I live in northern ca. I have a 30′ 5th wheel. Just rented it. Have the problem with water running down the side and on the roof? (also just discussed this today with my repair guy and he said that is a big problem should not be leaking anywhere and must be getting ready to go out!!!) See here that seems common and can be fixed. Well my concern from every kind of handy man to rv , tech and so forth. I have been told running these air units is going to cause me a fortune! MIN of what everyone is telling me is a 100 added to my pg&e? Is this true? I have heard they are so high to run no matter what and even with the most conservative person living in it. I am looking at every kind of other unit, from swamp for the window, to a small AC unit Enery affecient. What does anyone recommend. I seem to live in a town that you cant get honest answers no matter what from any kind of buisness person. Just they take your money, or try to sell you something else. I really want to know the honest truth about these air units which are on all RV and Trailers. HELP. Please respond to my email with any help. Thanks Maxine

  17. Klimaanlæg, I’m glad you found this of interest. Thank you for the kind word and for your input.

  18. Rock on, A separate independant powered air conditioner certainly would be do-able, but I don’t know if it would be practical. Thanks for your input.

  19. hi friends…
    r u ok…?
    A airconditioner is cool well.your AC unit is working well, and cooling,I would think a small roof mounted A/C unit powered by a small suitably sized gasoline generator would be one solution.

  20. Hi Cheryl, If your AC unit is working well, and cooling, there will be condensation coming from the unit. Your statement “My RV isn’t draining” leads me to ask, “where is it going then”. Your AC unit may require cleaning. I would have it serviced at a local AC service shop.

  21. cheryl

    my RV AC isn’t draining. Can you tell me how to locate the drain hole so I can be sure it’s clear? The unit is a carrier brand.

  22. Guy, It would be not possible for me to advise you on this given the information you provided. However, I would think a small roof mounted A/C unit powered by a small suitably sized gasoline generator would be one solution. The generator would have to be mounted in a well ventilated location with an unrestricted exhaust outlet outside. Best in an outside compartment.

  23. I have a large s.u.v. that I can not the a/c to work, have brought to every mechanical and electrical individual I can think of, can you advise if this small low profile will work on a s.u.v. that is a 16 pass, and can it be mounted to the roof, and since this item is A/C will it work in a truck situation or will I need some kind of power inverter, which I trying to avoid. Thanks for taking time to read this.

  24. Curt

    Could you touch alittle on theomstats for RV’s. I have a fiver TB and do not cool or heat the garage area. I would like to have a digital theomstat for better control of the living area.
    Would you think that Wal-mart would carry something like this or do you have a website I could look at.

  25. Sue Fritz

    Drainage is normal. To minimize the streaking on the side of your camper, purchase some inexpensive gutter extensions and attach them to both sides of your gutter on each side of the camper. We have found them to work well and they have basically eliminated dirty streaking down the sides of our camper.

  26. If a little bit of water bothered me that much ! I would have my RV dealers shop custom install a drain line on your coach to you liking.

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  28. While it’s normal for the water to run down the sides of the motorhomes and generally make a mess there is no reason it has to be this way. Why not drain the AC condensation into the black or grey water tanks or at least have some kind of drain tube to the underside of the motorhome. It’s ridiculous to me to have a $200,000.00+ motorhome and have it running water down the side of the motorhome leaving ugly streaks behind just cuz the manufacturers are too lazy or cheap to make them drain cleanly.

  29. xbombero

    Like most AC units water coming from the unit is common. The higher the humity the more water.


  30. alan richards

    I am a newbie and just ran the air for the first time last week. Is it common for water to flow off top of the RV while running the AC?