Air Conditioners and more Air Conditioners

Well, the past couple of weeks have seen a slew of air conditioner service- starting with a simply check out of a new (used) rig.

On this rig (1995, or 11 years old), everything checked out fine- standard cleaning of the LP appliances, testing 120 volt and 12 volt systems, leak testing the LP system, etc. Then I get up to the air conditioner. One glance at the filters, and I figured it would be a candidate for a good cleaning, and I was right.

On most rooftop air conditioners, you can see the inside (evaporator) coils by looking up through the air return- some models are easier than others, though. This was a Coleman Mach series, so I could just see the coils, but could not access them for a good cleaning, so a trip to the roof was in store.

Getting access to the evaporator coils is not very difficult, you do have to remove the plastic shroud, and then some sheet metal on the front-

Roof Top Air Conditioner- exploded viewThis is an exploded view of a DuoTherm BriskAir, but standard Coleman units are pretty much the same. A tip- when removing the screws that hold the sheet metal cover on, pay attention to the screws- there will usually be a few that have a blunt end on them, these are meant to usually go in to the electrical compartments, or where there are wires or tubing. You do not want to find out you put a sharp pointed screw back where it was not used originally.

Once you have the sheet metal cover off, I use a stiff bristle brush to “comb” any large lint off of the fins. Once the “big stuff” is gone, I use a good degreaser- I use VoomRV, because it is PH neutral and a great degreaser, Coleman recommends “Formula 409”. I tend to shy away from most commercial A/C coil cleaners as they are often very harsh on aluminum- they clean the aluminum coils well, but I don’t want the cleaner running down the side of the RV (something you don’t have to worry about in home units).

I soak the coils well, then lay heavy towels over the air intake to catch any water (I put towels inside as well- just in case), then spray the coils off.

This is a good time to check the drain holes for the condensation- there will be holes in the bottom pan on either side of the tray the coils sit in. It’s easy to clean them out. It’s also a good idea to check the gasket-
Air Conditioner gasket measurementmake sure the bottom of the unit is at least 1/2″ above the roof –

(images taken from sister sight- Bryant RV)

It is also a very good idea to check and clean the outside, or condenser coils. Sometimes they will be very clogged- as in the case from Dudes RV Air Conditioner page, but sometimes they might still look clean. Even if they do look clean- clean them any way! In air conditioners that have not been cleaned for a couple of years- and the unit has been used- I will consistently measure a 2 amp drop in current – just from cleaning. You will be amazed at the dirt which will come out of a clean looking coil.

While you are up on the roof with the shroud off, it is also a good time to check the fan motor- some units have oil ports- if yours does, put a few drops of electric motor oil in each port. You can also check the condenser blade. Another unit I serviced ( a DuoTherm) had a fan blade that was starting to go- it was cracking around the shaft attachment, which made it just a little of balance- to the point where it would hit the sheet metal every now and then.

DuoTherm fan bladeDuoTherm has redesigned the blade- the old models were 4 blade, the new ones have 6 blades and a much stronger center structure. They are very inexpensive, and used on nearly every BriskAir model. The part number is 3107914008 and if your local RV parts place does not have it, you can always order it from DTI RV Parts.

I’ve got to say- RV roof top air conditioners are about the most reliable component on an RV, but they do need regular maintenance. As with most things I talk about, given regular maintenance, they will give years of service. Often RV air conditioners are replaced simply to add new features and lower current draw, not because there is really anything wrong with them.

CC BY-SA 4.0 Air Conditioners and more Air Conditioners by Chris Bryant is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

20 comments for “Air Conditioners and more Air Conditioners

  1. Kris
    July 5, 2015 at 6:52 pm

    Have a Duo Therm 15,000 split unit (air & Heat) It is pouring water into the coach. It appears to be from the evaporator bulkhead.. It was working perfectly cleaned the filters ck the drain lines still cools well but water is pouring into the coach and down the walls on both sides..We are in middle TN and it is really humid…The coach was located inside a large horse barn but have recently moved it outside..Have dogs inside and need HELP!! Have cleaned the evaporator so many times the fins are smaller and it appears that the fan is pushing the water out of the pan directly into the room. Have not checked the bolts as others have said to inspect..Any suggestions??? Please contact me by email..THANKS!!!!

  2. Brian
    October 6, 2012 at 11:13 pm

    I am trying to install a White-Rogers 1C26 thermostat, I have a gray wire that was routed to the GL on the old thermostat. I need to know the cross reference for the gray wire. I have O, C, and A. Also should the red wire have gone to RH? Thanks!

  3. Dick stafford
    August 10, 2011 at 9:10 pm

    I have the duotherm brisk air and no matter what I try my coils inside the unit freeze up like a brick of ice . It cools great during the night when I go to work in morning then get home and it’s froze up I ve tried everything do you know anything I could do

    • August 11, 2011 at 8:17 pm

      The basics are make sure the coils and filters are clean. Run it on high, make sure the freeze sensor is in place and good, and make sure the cold air cannot recirculate in to the return.

      — Chris

  4. Terry
    May 23, 2011 at 12:04 am

    Anyone know where I can get a cooling unit, rebuilt, new or otherwise for a Dometic RM7030 RM 7030…I need an Amish one at a decent price.
    Thanks, Terry in Havasu.

    • August 11, 2011 at 8:20 pm

      The only Amish units I know of are from David Force at RV Cooling Unit Warehouse.
      He seems like a great guy with a great product.

      — Chris

  5. April 17, 2011 at 12:22 pm
  6. Ron
    April 16, 2011 at 7:19 pm

    I have an Emerson Quiet Kool Rooftop A/C Model 1100 unit and I am looking for a new motor for it. The model number is M15580 on the motor. Does anyone know where I can get one?

  7. Dave Mc'
    July 8, 2010 at 12:48 pm

    Hi — has anyone attempted to ‘route” a drian hose of a roof top AC unit. Mine is working nicely, but on humid Cape Cod days, there can be as much as 5-6 gallons of water puddling on the roof top. I’m worried that in time, it will eventually find it’s way inside. (I don’t want to “lose” my level on 26’ trailer to encourage run off.

    Thanks ! — DMc

  8. Sharon
    June 21, 2009 at 7:50 pm

    I have a coleman mach that has had the wires cut
    I would like to know what wires got back to each other

  9. Susan Ganzy
    May 31, 2009 at 6:15 pm

    Do you have any diagrams or recommendations on how to remove the fan motor for a Duo-Therm? One of the mounting brackets has broke off and needs to be rewelded. We have gotten as far as removing the 4 bolts that hold the fan motor in place, as well as removing the evaporator cover. Although loose, we can’t pull the fan out, there seems to be a collar inside a styrofoam area that is holding.

    • David H.
      September 9, 2009 at 5:31 pm

      Susan, I am having the same problem. Did you ever get an answer to your question?

  10. pj brown
    May 19, 2009 at 11:24 am

    i want to buy 15,000 btu unit

  11. Tom Keisling
    March 24, 2009 at 6:05 pm

    Do you know of a product to reduce the noise level on a rv a/c return air. I have been told of a product that is like a cover that drops down a few inches from return on a/c and draws air from sides to reduce noise level.

  12. March 13, 2009 at 3:15 pm

    Hi Joe,
    That’s a bit low, but certainly within allowable limits- the “standard” is a 20 degree drop, but high humidity will lower that quite a bit (and low humidity will raise it).
    One thing to keep in mind is the outside temperature- with outside temps much below 80, the inside coil temp will be below freezing, so some freezing is expected (and the freeze sensor should shut the compressor off if it gets too bad).

  13. March 11, 2009 at 12:03 pm

    Hi Joe,
    I would also check for leaks between the supply and return- this is pretty easy to do, just turn it on, let it run to it gets cool, then remove the filter and feel up in the air intake for any cold air that is leaking back through.
    The other thing would be checking the ducting, though you say that the airflow seems good.


    • Joe Zollo
      March 11, 2009 at 2:23 pm

      Hey Chris
      I will check for air leaks when I get home. Do you know what air temp is good ? I have been turning the air on lately with the vent open so it dumps the air at the unit and not threw the ducts.

    • Joe Zollo
      March 12, 2009 at 6:39 am

      Hi Chris
      We I took your advise again and did find some cold air leaking back. The difference between room temp and supply temp is about 17 degrees it just seems like it should be more and even after I duct taped the leaks the evaporator is still starting to freeze up on the bottom.

  14. Casey
    December 12, 2006 at 5:00 pm

    Great information. Will be cleaning my AC this spring for sure. Thanks.

    • Joe Zollo
      March 11, 2009 at 7:03 am

      Hey Chris
      I took you advise and cleaned the coils in my Duo Therm 13500 A/C unit but it is still freezing up on the bottom 2 inches of the evaporator after it has been on for a few hours. It seems to be moving the air ok but it does not cool the 5er like it should.It is a ducted system. Have any ideas what I can check next?

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