In some parts of the country, the heat is already here- in other parts, it’s well on its way, so I thought it might be good to talk about giving your rooftop air conditioner a basic tuneup.

A couple of things to remember about roof top RV air conditioners- all air conditioners work by removing heat (actually, all refrigeration works that way- as do heat pumps), and RV air conditioner- as they come from the factory- are hermetically sealed, and they only hold about 1 pound of refrigerant (at this time, R-22 is the refrigerant used). The point of this is that with less than 1 pound of refrigerant and a sealed system, 99% of the time, “not enough cooling” complaints are due to air flow issues, and not lack of “Freon®”

Luckily, the average fix for this is easy- clean the coils! Let’s take a look at how to do this….

These procedures do involve some risk- you will be working on the roof of your RV, and working around 120 volt systems and devices which can store power even when shut off.
Always observe all common safety procedures!!

Unplug the rig, disconnect the battery, don’t fall off the roof…. you get the idea!

A word about RV roofs- most modern RV roofs are plenty able to support a person walking on them, but use your own judgment- if the roof seems springy, lay a piece of plywood to walk on, and if the roof is an EPDM roof, take care to not damage the membrane- make certain your feet are clean, and pick up your feet before turning them (which causes bubbles)

There are some basic and some advanced maintenance items that can be performed on roof top air conditioners- I will mention some of the advanced items, but illustrate the basic ones.

To get an idea of what we are dealing with, I’ve drawn a “typical” cross section of a roof top air conditioner:

The first basic area is the air filter. In summer, using the RV and air conditioner around the clock, the filter should be checked weekly and cleaned as needed. RV air conditioners use either a foam type filter or a fine mesh, both of which can be rinsed in water and reused. I cannot stress this enough- keep the filter(s) clean!

After a few years, even the best filter will let enough dirt past to coat the evaporator coils, though, so they need to be cleaned. If the coils are not too dirty, and if the installation leaves enough room to access the coils, you can simply buy a can of spray coil cleaner and use that- saturating the coils, letting it sit for a bit, then running the air conditioner so that the condensation will rinse the coils off.

A tip though- be very careful in choosing a product to use- a lot of commercial coil cleaners such as would be found in home center type stores can be pretty strong- not something I would like to run over the outside of my RV, so I only use Enviro-Chem coil cleaner, specifically made for RV use.

But- sometimes the coils are just too dirty to simply be rinsed off like this, or access from the inside is restricted enough that a trip to the roof is needed.

The 2 most common models are the DuoTherm Brisk Air and the Coleman Mach series , though the cleaning methods will be the same for every brand and model.

The first task is to remove the shroud- either screws around the base of the plastic (DuoTherm and Carrier), or screws in the top (Coleman).

Once you have the shroud off, you have to get to the evaporator, which is at the front of the unit under a (usually) sheet metal (sometimes styrofoam) cover.

The evaporator cover (if it’s metal) will be attached by a number of sheet metal screws, remove these, but pay attention to the screws as you remove them. On some models there will be either different length screws, some screws might be blunt ended to go in to electrical areas. Just pay attention and replace the screws in the same way they were removed.

Once the cover is off, you can see the evaporator coil. Note in this picture, the “freeze” control is not installed in the proper place (only ducted installations use a freeze control).

Now it’s simply a matter of cleaning the coils. Coleman recommends “Formula 409”, I use VoomRV, which is a ph neutral degreaser.

Soak the coils well- if there is a lot of crud on them, I use a bristle brush to clean the coils- carefully, as the fins are delicate, to scrape off the crud. Another option is using a “fin comb”, which is also good if the fins are bent, restricting the air flow.

While these coils are soaking, do the same thing for the condenser coils- soak them well with the cleaner. I can usually measure a 1 to 2 amp decrease in current draw simply by cleaning the condenser coils- this on 1 to 2 year old air conditioners.

Next comes the tricky part- rinsing the evaporator coils without flooding the rig. It’s not hard- put down towels in the air return opening, and don’t use too much water pressure- the cleaner will do the work, you just have to rinse the coils off. Do this on both evaporator and condenser coils.

A couple of advanced items- when I do this service, I also will check the gasket to make sure it’s still in good shape, I will check the current draw on the unit, and I visually check the electrical connections to the A/C electrical component – the start and run capacitors, etc.

And…. that’s it! Button everything back up, and know that your air conditioner will be able to take as much heat as possible out of the inside through the evaporator, and get rid of the heat through the condenser.

Leave a Reply


  1. Tonylyn

    Note that when there is a wide temperature dierffential, e.g., when heating a house on a very cold winter day, it takes more work to move the same amount of heat indoors as on a mild day. Ultimately, due to Carnot efficiency limits, the heat pump’s performance will approach 1.0 as the outdoor-to-indoor temperature difference increases. This typically occurs around −18 b0C (0 b0F) outdoor temperature. Also, as the heat pump takes heat out of the air, some moisture in the outdoor air may condense and possibly freeze on the outdoor heat exchanger. The system must periodically melt this ice. In other words, when it is extremely cold outside, it is simpler, and wears the machine less, to heat using an electric-resistance heater than to strain an air-coupled heat pump.

  2. Andy Nixon

    The A/C unit in my motorhome is used every two or three months. I ran it about a month ago for several hours and had no problems. I ran it again last month and it ran fine for about 1/2 hour and the fan stopped blowing. I took the inside cover off and spun it by hand. Now when I turn the fan on I have to give it an initial spin and it will turn on its own but only at a very low speed. It does turn faster when I turn the switch to high but not nearly as fast as it should. Any suggestions on what the problem is?


  3. Andrew Eastmond

    I cleaned everything I thought and still had freeze up. I then looked at the blower fan and it was greatly restricted. There was dirt in every fin on the fan. I got a long thin weapon and gently scraped each gap in the fan and now I have no freeze up any more. Thought it might help someone

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  5. philip alexander

    I have dometic heat pumps on a newmar dutch star which has a long duct system. wondering how to catch the water if i rinse the evaporator coils. seems like rinsing would fill the ducts. very good article, I have cleaned the condenser often but not evaporator. please email answer.

  6. David

    I have A question about replacing our Dometic Duo Therm 13,500 btu ac. We want to replace it with a 15,000 Dometic brisk air ac. Our 13,500 is ducted and so is the 15,000 we want to buy, but we’re not sure which direction the duct runs on the 15,000. On our present ac the duct runs straight out the center of the back and runs straight to the rear of the rv. I’m just not sure how to know if the new ac duct will match up to it.

  7. John Jordan

    Does anyone know where rv condensate drains from the A/C are, shouldn’t a drain line be installed with the AC unit?

  8. Brenda

    Hi this is a going to sound like a really strange question but I really need some help with it. I live in a RV full time in the desert. Sometimes in the area I am in they spray chemicals to kil weeds that make me sick. What I am wondering can the outside air come into the RV more easily with the air conditioning on?

  9. Bobby

    I have a ducted Coleman A/C that seems to have a problem. I bought this 5th wheel and when I first plugged it in and turned on the A/C, it came on fine (both fan and compressor started) then after about 10 mins the compressor cut off and the fan continued. This was with temperature around 95 degrees. The compressor never came back on after that. So, I followed your directions and installed a new filter and cleaned both evaporator and condensor. When I ran it again, it was now around 85-90 degrees (late evening), it ran for around 35 minutes until I had to leave so I turned it off. The next day, I turned it on when outside temp was around 90-95 degrees and it ran without cutting off for 1 hour and 16 minutes and then the breaker tripped and the unit cut off completely. I checked the breaker box and reset the breaker but noticed it was very hot. I also sprayed the thermostat housing and all switches and the board inside of it with electronics cleaner which appeared to help the thermostat function a bit better but why would the unit trip the breaker like that? Also, the freeze control appears to have been pushed into the middle center of the evaporator coils. Could this be causing a freeze problem? I would appreciate any help and direction you can give me to try and fix the problem. I have another A/C that I can replace it with but would rather fix this one if I can. Thanks in advance. – Bobby

  10. Paul

    I have a Coleman Mach III PS 13500 BTU ac. It works wonderfully at night but just can’t cut it in the daytime.It worked better when it was new than it does now (90 degree plus heat). It hasn’t improved even with a recharge. The coils are clean and everything else is right. The last one I had quit when the compressor went out. This one just seems to be unable to keep up. Is it new a/c time or is the heat just too much for it?

    Whats the top best rooftop A/C you can buy? It doesn’t seem to be Coleman.

  11. Dwayne Mcintyre

    My Rv A/C Is a 15000 duro therm comes on and runs fine on high for about 5 to 10 mins and fan stops but compressor in still running … So I cut it Off and wait a while and can go back and its run again about 10 mins and fan shuts off but compressor still runs… BUT if I turn fan on low cool it want cut off untill I turn A/c off.. Fan seems to spin freely when turned by hand. with on play or noise. A/c cools good when its running. Thank for a Little help IN Advance

  12. Chris Bryant

    Hi Kim- while it’s possible the compressor is bad, that’s really not something that happens very often- it’s probably either a wiring problem or a bad start capacitor/start device.

    Hudson- it sounds like the compressor relay in the control box is sticking- you can try the “quick and dirty” method of removing the filter (the box should be at the front) and giving it a good whack, but you will probably have to replace the circuit board- not a terribly expensive part.


  13. hudson

    I have a Bounder and the thermostat was in off position, but while stored the A/C came on and we cant get it to cut off except to turn all breakers off. What can I do to fix it?

  14. Kim Chambers

    Hi i have a question about a ac unit. I have not used the camper all winter, We took it out to a campground and plugged it in. And the fan works fine, but when you turn on the ac in does let the compressor kick in, checked the voltage, and and amps, got enough,, good the compressor be bad? How can you check that? Trying to save a few bucks here,, it is insured, not sure though if the insurance would replace ac unit though, thanks for any help.

  15. barry

    I have a ducted A/C dometic penguin unit and wonder what would I need to do to clean the coils. Do you have to remove the unit from the opening to access the inner condenser coil? I cannot see the A/C unit from inside as it is ducted and the filters are just foam pads about a 1/4″ thick and 5″ in diameter. I have taken these down and rinsed them out but they don’t seem like a very good filter medium, any other filters out there that are any good? My unit is 2 years old and probably needs cleaning so any help or ideas would be appreciated.

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  17. Jackie

    I have a Coleman RV Roof Air Cond. It is air cond only and no heat. The problem I’m having is when I turn the air cond all the way off, my compressor keeps running. If I turn the thermostat to “warmer” it will finally stop the compressor from running. ( even with the air cond turned all the way off now ) I have had the air cond turned all the way off for at least 10 min’s or sometimes longer, and all of a sudden my compressor will start running while my air cond is turned off.. I ordered and installed a new thermostat switch, but it is still doing the same thing as before. I have good cold air anyway. Any ideals what I might check next, and if so, maybe tell me how to do it? Thanks, Jackie. [email protected]

  18. Christine

    Need help. I have a Duo Therm Dometic unit I have replaced the Thermostat, control board, and one of the compasters. The unit will not cut off. when it reaches a certain temp. the only way it will cut off is switch the hi low switch to low and it will cut off. It will not cut off by the cool off heat switch. When it reaches a certain temp the fan will switch from high to low . Please email me back with some suggestions I don’t know what else to do. Thanks

  19. Reynz

    Found a cleaner, follow the link below…

    Enviro-Chem A/C Coil Cleaner 38-1706
    Save energy and make your air conditioner more efficient by keeping the coils dirt and grime free. Just spray on – no rubbing or high powered spraying needed. Leaves a nice deoderizing fragrance on coils. 20oz.

  20. Marcus Gordon

    well can anyone help me with A Rv rooftop air conditioner coleman it’s not got any airfilter the inside has alot of dirt and crud on the inner coil I think that right so would this cause it not to stay on it clicks on and back off in about 2 mins and there is cold air coming out .

  21. TakerEasy

    Great article Chris. I would like to mention, this is the perfect time to check a couple of other items while you have the covers off.

    1) Condensate drains, make sure the drain holes from the evaporator catch tray are clean and flow, as well as the drain holes in the A/C’s bottom tray.

    2) Inspect and remove any mud daubber nest from the fans and shrouds, if your in an area that has mud daubbers. They can cause noise, vibration, and take out the motor from running out of balance.

  22. Sam R


    I need help. I have a Duo Therm rooftop airconditioner. It is Freezing up on me.I replaced the Freeze Controland cleaned the coils,unfortunatly this did not help. It does blow cold air but still freezes up.

    What other parts might cause this problem to persist?

    Thanks for your help


  23. Khim R Kite

    I have a Coleman Mach Series on my 30″ Travel Trailer.I removed the four screws that hold the shroud on,but was still unable to remove it.Am I missing something? Thanks

  24. Terry Rhodes

    If your ac cuts off and on often. check your thermostat and see if air is coming out from behind it.I have a 06 Jayco Eagle tt and i felt air coming from behind the thermostat when the ac was on.This was makeing the ac cut off sooner. I took the cover off and found a large hole where the wireing comes through,and the ac air. I cover the hole with (rv’s best friend) duct tape.Now it stays on till it reaches temp. Note do not use metal tape,It could come loose and short out your unit.

  25. Gene Morrow

    I have two Coleman Mach a/c’s. They are on a 1999 RV. On a recent outing, both were running 24 hours a day. One of them quit cooling. The fan would run but the compressor would not engage. We also smelled what seemed like burning wires. I have checked the wires in the coach under the A/C and did not see any signs of burned wires. I took the cover off the A/C on the roof and saw not signs of burning. I did not take off any metal covers to check further. Any suggestions?
    Should I take it to a repair facility? The outside temps at that time were in the 90’s with high humidity (South Alabama).

  26. Hi David,
    Good point! The one I have pictured is the older style with clips for the tubing- these didn’t work as well as the new style which does clip in to the center of the coils.

    Rickie- the only problem I have with standard A/C coil cleaner is that in a house air conditioner, the condensate will drain out on to the ground, but in (most) RVs, the condensate has to run over the roof and down the sides.

    I’ll be getting more EnviroChem cleaner the day after tommorow- I’ll have a look at the ingredients (a google for the msds on it turned up zilch).

  27. DavidJ

    Excellent Article! The only comment I have is about the freeze coil. Dometic customer service told me that it should go on the bottom center of mine against the coils. It even has a little indention for it there. Just something to check. I’m sure it would work in either place. Mine hasn’t frozen up since I fixed it.

  28. Thank Chris! Here is the other question about the cleaner. I am little concern about the enviro chem cleaner. The reason why is because I do not know if the cleaner has petroleum. If it does, it will harm the rubber roof. Do you use the cleaner for both coils – evaporator and condenser? I would think you can buy a can of cleaner at any a/c service center. I do not think it has to be use for RV only?

  29. Hi Rickie,
    The easiest place is at the 120 volt breaker panel, where the black (hot) air conditioner lead will be searated from the neutral and ground.

    Michael- the EnviroChem product is hard to find online (I couldn’t find it on Camping Worlds website), but I did find it here, and most RV shops should have it.

    That said- if you are going to dig in to the units, Formula 409 works fine- the EnviroChem coil cleaner is best if you just want to clean with out taking it apart.

  30. Michael

    Your excellent instructions and pix have motivated me to get up there and clean my rig’s ACs. Where would I find the RV-specific cleaners you mentioned?

  31. Chris I have a clamp meter that has amp reader. I am trying to find wire. where did you use the meter to measure amp?