Making the RV Significantly Colder – An Air Conditioner Mod

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A couple days ago, Stef offhandedly posted a picture of me tinkering with the RV air conditioner on our Facebook page. Nothing new, she posts loads of pics of what we’re up to day to day there, and many of them involve me working on Lance.  I didn’t think much about it, but apparently, many of you left comments and were interested in what I did and if it worked.  The quick answer is: I adjusted the thermostat and yes it worked.

But before you go trying this yourself, here’s the situation I had:

  • Our new air conditioner, a Dometic Penguin II, works very well and produces a temperature differential (intake vs. cold air) of about 20 degrees.  So the air conditioner was not “broken”.
  • With the thermostat (the colder/warmer knob) turned all the way cold, the air conditioner would cool the inside of the RV to about 76 degrees.
  • Once the temperature was 76 degrees, the compressor on the AC would stop running.  The fan would still run, but it was no longer cooling the air.  When it warmed back up to 78, the compressor would kick on again and cycle with the temperature.

In my mind, 76 degrees is not “coldest”.  It’s not even “cold”.  In fact it’s uncomfortable.  If you’re sitting on the Ultraleather dinette next to a window in the front of the rig, and the temperature is at 76 in the back of the rig – you’re going to be sticking to the seats.  Not cool (ha!).  So, I decided to change the air conditioner’s minimum set point from 76 degrees to something considerably lower.


A Word of Warning

The air conditioner manufacturers have the minimum temperature set in the mid-70s for a reason.  They don’t want your air conditioner to “freeze up”.  That could prevent the AC from working, damage the air conditioner, or lead to a service or warranty call.  They don’t want any of these to happen, so they deploy their air conditioners at temperatures that will make you sweaty – but will guarantee that the unit never freezes up.

ca. 1602 --- The Maiden and the Unicorn by Domenichino --- Image by © Alinari Archives/CORBIS

Back in the 1600s, they had air conditioners that froze up.

I’ve always regarded the “air conditioner freeze up” as a myth.  I think it’s the same kind of reasoning that gives us RV shower heads that leak all the time on purpose – because there’s an extremely remote chance you could scald yourself if it doesn’t.  (By the way, I fixed that problem too, and you can read all about that here.)

Of course, I should point out that we live in Utah, where the relative humidity typically hovers in the single digits.  We don’t even get condensation on the outside of an icy glass.  So the chances anything would “freeze up” on me in the middle of summer are basically zero.  If you live elsewhere, you may want to take that into account.

But back to the AC.  There are four main reasons your air conditioner may freeze up:

  1. Insufficient airflow across your air conditioner’s evaporator coil.
  2. Your air conditioner is low on Freon.
  3. You are running your air conditioner when the outside air is below 62 degrees.
  4. There is a mechanical failure (kink in refrigerant lines, a blow fan is not running, etc.)

Number 1 is something you can prevent by keeping your air conditioner’s intake screens clean, so put that on your routine maintenance checklist.  Numbers 2 and 4 represent problems that I’d like to know about – and a frozen air conditioner seems like a good indicator.  And number 3 is something I’m not worried about because I’m not stupid.  So even if I did believe in air conditioner freeze-ups and Bigfoot, I think the problem is manageable at best, and just an indicator of a bigger problem at worst.


What I Did

So, if you think you have the same problem with cycling that I did; you think your air conditioner is unlikely to freeze up; you don’t have a separate wall thermostat for the air conditioner; you can use a screwdriver; and you’re unafraid of possibly voiding your AC warranty, here’s what I did.  I have tested this procedure on my own AC unit, which is a Dometic.  I suspect that others (Coleman, etc) may be similar, but I have not verified this.

First, obviously, make sure that ALL POWER to your coach is turned off.  No generator.  No shore power.  No inverter.  And I even shut the batteries down for good measure.

Then, remove the indoor air distribution box (ADB) cover.  You’ll wind up with something on your ceiling that looks more or less like this:

What you’re looking for is the inside part of the “colder/warmer” knob – the thermostat.  It will likely be inside another metal enclosure inside of the ADB.  In the picture above, I’ve loosened the cover on this interior box.  If you’re stumped, it will have a strand of copper leading into it.  The other end of that copper is on a probe in the intake air.

Once you’ve located the thermostat, do what you need to in order to remove it from the ADB.  In my case, I had to remove two screws.  But your air conditioner may have nuts or some other way of holding it still.

With the thermostat removed, you’re looking for an adjusting screw of some sort.  It probably won’t be labeled, because they don’t want you messing with it.  But it should be there.  On my Dometic, the screw looked like this:

Now, for the tedious part.  In small increments, start adjusting the screw.  You want to do this slowly:

  1. Adjust the set point screw ¼ turn.  (I don’t know which direction on yours!)
  2. Reassemble the ADB box (Safety first!  You’ll be turning on the power.)
  3. Run the air conditioner until the compressor cycles
  4. If it gets cold enough for you, you’re done.  If not  – lather, rinse, repeat.

In the end, I gave my screw about one and a half turns clockwise.  When I had finished, the “warmest” setting on the thermostat gave me about 80 degrees at the dinette, and 68 degrees at the dinette was at the ¾ mark.

It’s important that there is *some* realistic temperature where the air conditioner will cycle off, and that temperature is at 62 degrees or above.  So don’t overdo it!

And with that, I was done.

This took about 15 minutes to figure out, and about two hours to do with all the setting and checking.

Good Luck!


James is a former rocket scientist, a USA Cycling coach, and lifelong fitness buff. When he's not driving the RV, or modifying the RV (or - that one time - doing both at once), you can find him racing bicycles, or building furniture, or making music. In his spare time, he works for a large IT company.

    107 thoughts on “Making the RV Significantly Colder – An Air Conditioner Mod

    1. Brad

      Is there a similar solution for a ducted AC?

      We did this for.our Coleman Mach 3 on our previous Class 3. It worked great.

      I went about 1 1/2 turns counterclockwise.

      1. James - Post author

        In a ducted AC unit, the temperature is usually controlled by a separate wall thermostat. Our current wall thermostat is digital, so any bias setting would have to be programmed in. For an “old school” mechanical thermostat, there probably is such an adjustment, but I can’t say where it is, as I don’t have one to tinker with.

    2. Kevin

      Been putting this off for way too long. Not this summer! Worked perfectly for my Dometic 15000 btu.
      My experience was turning the little screw about 1/2 a turn clockwise! Thanks for the info James!

      1. James - Post author

        Another winner!
        So glad you found this and that it was helpful to you.
        Nobody should have to sweat while looking at a running air conditioner.

        1. Felicia

          hello I was wondering if you happen to have the wire diagram for the control panel for the RV ac domestic brisk air 2 ?

        2. James - Post author

          I don’t, I’m sorry.
          If you dig around the internet long enough, you can probably find the diagram you seek, though.

    3. Ed

      “Freeze up” means that the condensation water on the face of the evaporator fins has frozen because the temperature of the evaporator fins is below 32 degrees Fahrenheit. Once some water freezes, more and more ice will build up, so air flow through the evaporation will keep decreasing as more ice builds up. As the air flow decreases, the evaporator temperature will go down, thus promoting more ice build up. The insufficient air flow will reduce the amount of heat exchanged from the air to the refrigerant, so the refrigerant may not fully evaporate and may return to the compressor as a liquid which can damage or destroy the compressor. Compressors are designed to compress vapor/gas, you cannot compress a liquid. This is try of any HVAC or refrigeration system. Air conditioner manufacturers may use a separate temperature sensor to detect freeze-up of the evaporator, or a low refrigerant pressure switch to protect the compressor from taking in liquid refrigerant, or other methods to protect the compressor. However, if you mess with the system you could have an expensive problem.

      1. Dean Hauser

        that’s a very well explanation of how a ac unit works but, in a hot tin or fiberglass box when it’s 95 degrees out and its 85 inside of the box you want the AC unit working as it would be working in your house, car or any other place you can adjust the temp. So if you mean “mess” with the system as a warning to leave it as a mediocre working system, that’s not realistic, keep your coils clean and washed out so all the air that was intended to flow through the unit will do so you won’t have problems most like, of course low Freon is another issue. My front ac work as should getting the temp down as needed but, the bedroom ac compressor shuts off way too soon so, this article was a great help since the qc at the factories probably wasn’t spot on as usually is the case

    4. Jim James

      I have an 80’s RV that I rarely use only for hunting, what Id like to do is maybe just just off the tip of the copper tubing sensor, what would happen if I did that. Essentially deleting the thermostat? Will air blow all cold all the time which is what Im after. My RV leaks all over so having a thermostat that’s set to 76 is really pointless and creating it to cut on and off every few minutes it never gets cool. What happens if I just cut that copper thermo sensor or find a way to unscrew it> Deleting it? Thanks!!!

      1. James - Post author

        Oh wow. I really don’t know what might happen if you cut that off.
        It could either fail open or closed, meaning the AC would run either all the time, or never.
        I’d have to look at a schematic for your particular model to figure it out.
        Sorry I can’t be more help! Maybe an HVAC technician might be a good one to ask?

    5. Dave

      Hi James, Just wanted to add another “Thank you!” for this article. I swapped our old thermostat-controlled and ducted Dometic unit out for a new direct discharge Dometic Brisk II specifically so I could try this fix. Wow, what a difference! For the first time, I have an air conditioner that actually cools things down to a comfortable temperature. (My wife is complaining it’s too cold, which is how I know it’s about right.) For what it’s worth, on our unit turning the adjustment screw clockwise caused our compressor to cycle off more frequently, and turning it counterclockwise caused it to cycle off less frequently, allowing the temperature to get colder.

        1. Dave

          Hmm… well, I was in your camp as far as freezing being an unlikely issue on a warm day in the Rockies, but after running for about 4 hours (85 outside, Low 70s inside) the evaporator coil froze up completely from top to bottom. Blower working fine and brand new unit, so coil is very clean. Guess we’ll have to back off on the adjustment screw and see what we end up with.

        2. Matt

          So, if I’m understanding correctly, This is not something you can try if you have a wall thermostat?

        3. James - Post author

          Well, I honestly don’t know. I haven’t tried it with a wall thermostat.

        4. Joe Green

          You do know that “Bigfoot” isn’t a myth & is actually a thriving species, don’t you? I’m serious.

    6. Pete & Brenda Bena, VA

      Thanks for this information. Somehow I read past your instructions to go 1/4 turn at a time and went straight to 1-1/2 turns clockwise. Needless to say I spent my time backing out the screw and in the end am somewhere near 1/4-1/2 turn clockwise. In the end I am so much happier with the performance of the unit. Thank you again!

        1. Jacoby

          Thank you very much for this article!! When I opened mine up, I discovered that the person who installed in failed to put in the air divider. I had an issue with my air conditioner short cycling. I installed a micro air easy start and it wouldn’t work properly because the compressor kept turning on and off way too soon for the device to register the 5 starts that it needs to learn the compressor turning on. Hopefully when I get the air divider installed, the screw trick works for me too. I called customer service and spoke with a tech and asked about that screw and they said they have no idea what it is lol. Thanks again for such a well written piece!

      1. Jacoby

        Just an idea… can you just turn the screw in all the way and let it run until you reach a desired temp in the RV and then start backing out the screw until the compressor kicks off? Or is that not something that’s instant?

        1. James - Post author

          I never tried that, but I get it.
          Our current unit has a wall thermostat, so I can’t try it.

    7. John

      I took my thermostat out and used a relay so I could connect it to the RV house thermostat. Then I added a time delay thermostat to start the fan 3 seconds after the compressor to reduce the starting load.

      1. Jacoby

        What is required to remove the manual thermostat that is referenced here and turning it into a digital controlled one?

    8. Johnny

      Thanks for the information
      I bought a new 15.5 for bed room Brisk 2 ac Compressor cycles to quick too cool I will try it
      Thank you very much

        1. Yogi Armstrong

          I live in Florida and just bought an 06 Pleasureway (my first rv) and the Dometic Penguin doesn’t get cool enough for me and cycles off. I did ohms test on all the caps, continuity on ptcr and ohms test on compressor. On the compressor ohms I got this, Com to Start 3 ohms, Common to Run 1.1, and Start to Run 3.7 (Don’t know if that means I got a failing compressor or not, I’m a welder not an AC guy, lol. I want an AC that freezes me out. I’m going to try your hack tomorrow, keeping my fingers crossed. Great webpage!

    9. Chris

      Thanks this is just what I was looking for, I just installed a new ABD on a older 13,500 btu Dometic AC unit we had that was in good working order that we had swapped out from another trailer we owned. I am using this in the bedroom of our Wildcat fifth wheel. Every thing went well but the factory set point for coldest output was way to warm. Your how to is what I needed to get the old AC unit to work with the thermostat on the new ABD and cycle the compressor long enough to cool the bedroom with out freezing up.

    10. Tom Crawford

      I’m a little late to the party but just tried this on my Coleman Mach 8. Purchased the AC a few years ago but just had it installed on a ’68 Oasis. It wouldn’t cool below 76 and kept cycling the compressor. Tried your solution and at first not much success. Once I turned it about 2.5 turns counter clockwise – BAM! Got it to run continuously till 71 degrees and would have probably gone more. No insulation on this camper and the Texas sun does a good job staying ahead of the AC but at least it blows cold and doesn’t cycle till I want it to. Wish I had an Auto AC thermostat instead of just low/high cold. Thanks again for the great tip!

      1. James - Post author

        There must be a lot of hot RVers out there, because this post has had a resurgence in popularity.
        Glad people are finding it, and glad that it’s helping people keep cool!


        thanks for the tip, i have coleman, just bought a 1 yr old toyhauler and here in texas it does not cool below 76 degrees. I will give it a shot this weekend and see how it goes.

        1. chris wienken

          so, after I taped up all the vent sleeves to the duct work the air blew much harder. taped up the air divider between return air and forced out air, it was sitting at a 45 degree angel. did that last week. this morning I adjusted the thermostat screw counter clock wise but did not notice it any colder. I was very hot and humid today. air in was 80, air out was 60. seemed cool in the rv, but thermometer showed about 78 at 3pm. its was 68 inside the rv at noon. any idea if counter clockwise is the correct direction to turn the screw. i also put 1 1/2″ foil backed foam in the 2 skylights bathroom vent. we have a toy hauler and had a 3 season tent system for the fold down door porch. I’m afraid once we use it I will not be cool enough inside the rv.

        2. James - Post author

          Not sure on your particular make and model of AC exactly what’s the correct way to turn the screw to get a colder set temperature. Can’t hurt to try it (as long as you put it back if it doesn’t work).
          Sounds like there were other problems with your install. It may be smart to have the whole unit checked out.


          OK, Update on Mach 3 in toyhauler. I turned the screw 2 turns counter clockwise, based on the guy that had a Mach 8 and turned clockwise. Last night is was warm and humid in east Texas, the RV cooled down in about 30 minutes but this morning it was not blowing out the vents and was a little muggy in the RV. It has frozen up, I could not get it to freeze up last weekend durning the day and this was the first time running at night after the adjustment. The compressor did not seem to kick off at all so maybe I went a little to far, but I should be able to control that with the warm cold knob. I called Coleman earlier this week for some technical help and they would not even discuss turning that screw. Oh well, I will get it dialed in and keep yo posted. We are also thinking about a 2nd portable ac unit as we have porch system for the tailgate and a tent room, so i know that will kill the effeciency of the ac. Thanks James for all your good advice.

        4. James - Post author

          It sounds like you may have been too aggressive with the set screw.
          Backing off a bit will probably help prevent the icing up.

          Good luck!


          UPDATE: this has been trial and error for sure. When running on Cool High and the temp knob about half way if freezes up at night, during the heat of the day it does not freeze up. However if I run on Low Cool with the temp know half way it runs great, no freezing up at night and the TT gets very cold inside. During the day it is comfortable, I would not say that when it is 95 to 100 degrees out side with high humidity that it gets cold, but it is better. Considering a small plug in A/C unit so when we open the tail gate and use the 3 season tent it will help us keep cool during the day. Thanks for the all the advice James, I may turn the screw back just a little, maybe a 1/2 turn, but i think we have the problem solved. I do realise there is only so much the AC can do on those extremely hot humid days.

        6. James - Post author

          Glad to hear you’re making progress and mostly (it sounds like) resolved.
          That’s one of the things we like about living in the desert southwest… virtually no humidity!

        7. Kevin Sparks

          Hi, Christopher. If you’re still on here, do you remember which way you ended up turning your t/stat screw on your Mach III? Thanks!

      3. Eddie Rose

        Thanks for your comment, I have struggled with my 5th wheel bedroom A/C since new (4 years now). Also a Colman Mach A/C. It had been back to the dealer twice, they had checked the duct work the first time and found where it wasn’t quite taped in properly but it still cycled and and wouldn’t cool below around 74 degrees so a second trip to the dealer. This time the dealer replaced the thermostat but that didn’t change anything. I was flabbergasted, my 5th wheel is a four seasons very well insulated RV just didn’t seem right to me. Came across this article while on a camping trip so I don’t have a thermometer to see what it’s getting down to now but after following the advice in this article and the comment tip 2 1/2 turns counter clockwise I’d say it’s well into the 60’s now, I actually had to turn the temp knob up for the first time ever, the wife says you could hang beef in there now! Lol thanks so much, we can now have a comfortable sleep at night

        1. James - Post author

          Yess!!! Another happy RVer!
          I’m so glad that this post is enjoying a resurgence and helping so many people!

    11. Mark Pate

      Greetings, Great Article. I just installed a Brisk Air 15K BTU, I also thought it was not performing as well as the 45yo Dometic Sur Start I had just removed. I have a tech request in to Dometic, no response. I can see the manual thermostat does not want to cool it below 77deg, I thought there was something wrong. A second question, which I have sent to Dometic, is the cycling issue. When this this is trying to reach minimum temp the compressor is staying on about 1:05 min and off 0:45. when it reached 77d, the compressor ran (+)(-)0:30 and the fan ran for (+)(-)2:00, This is a brand new unit with 121.5v going to it on a dedicated circuit. There’s not much way I could have messed up the install, it took me longer to scrape the gasket off the old unit than to install the new one.The Sur Start I took out was cycling the same way. Both are cooling the trailer (’66 26″ Airstream) adequately, I thought the old one was short cycling on me.

      1. Jerrick

        I am currently experiencing this exact issue. When my minimal temp is reached and the unit tries to maintain the set temp, it will start to short cycle on me and cause my generator to overload (and probably damaging my compressor at the same time). I am not sure why but my coleman mach 15k btu apparently does not have a built in delay mechanism that prevents the compressor from kicking on before pressures are equalized. after hours and hours of digging around various forums I came across a device called a delay on make timer that you can install on the thermostats cool call wire (yellow i believe) that prevents the compressor from kicking on until a predetermined amount of time has passed.

    12. Jerrick

      I just happened to come across this blog while searching for a different RV AC related issue that I’ve been experiencing. While it didn’t help me with the issue I’m having, i certainly can appreciate the time and effort you spent in making up this tutorial. I’m new to the camper life so I have a lot of learning to do still. St. George is my home so I’ll take any tricks you can offer in keeping cooler in the summer.

    13. phil

      My unit was short cycling. I found the thermocouple pushed out of the air flow, essentially behind the flange, so it never tested “ambient” air temp, only influenced by leaking cold air.


      Wow!!! Such a simple fix!
      I just purchased a new Dometic Brisk Air 2 to replace the one in the front room. However it just didn’t blow cool enough. Now thanks to you the air blowing out is 65*F

      THANK YOU!!!!!

        1. Patricia

          What about if you have a separate thermostat but still believe the 2 yr old in doesn’t not blow out cold enough air

        2. James - Post author

          Hmmm. In that case, I’d probably look at the programming for the thermostat to see if there was a way to make it think that 70 degrees was 80… You might need to look at the installer manual for your separate thermostat.

    15. Dan

      AC coil will freeze up. I had one do it at amy house. The cause was lack of airflow. I live in Michigan a very humid state in the summer. If you keep everything clean there will be no problem.

      Thank you for your post. I was thinking something was wrong with my rv ac as it would only get to 76 deg. I cant wait to check this out and see if it fixes mine.

    16. Dcblue

      We did the same thing and it seemed to work. I unfortunately turned too much the 1st time and the screw came out of the spring. No big deal we ordered another. Question is do I have to rotate knob either way hot or cold direction prior to turning screw or just give it a turn and repeat? I saw another YT vid where a guy used a meter etc and turned the knob to a certain point first. Necessary or no? Installing the new one today.

      1. James - Post author

        I don’t recall having to set the knob to a particular position before doing this.
        But I’ll also say that before doing this procedure, we almost always had the dial “all the way cold”.

      2. Jacob Wright

        The temperature probe that comes off the thermostat…is it supposed to be stuck in the coils? Had a mobile guy come to my rv due to ac freezing then not cooling great and he said it was because the probe wasn’t in the coils. I call bs because we have had it over a year and it just started doing this. What is your opinion

        1. James - Post author

          Well, there’s a “Freeze Sensor” that actually is supposed to be embedded in the coils. But it’s just wedged in there…
          Perhaps it fell out over time. I suppose it’s possible the service guy was just using the wrong term.
          Can’t say for sure, wasn’t there.

    17. Bill Dunbar

      So am I understanding that you do not have a wall thermostat? If so would this work with wall mounted thermostat?

      1. James - Post author

        Correct. Our rigs do not have wall-mounted thermostats.
        The interior air distribution box will be different on a unit with a wall thermostat. As I don’t have one to look at, I can’t say if the procedure here would work or not. You’d have to open yours up to see if the mechanics were similar.

    18. Chris

      I adjusted my 13,500 btu dometic using your suggestions, exact same thermostat, same amount of turns. I am able to get the inside of my unit to 62° which definitely will help during the summer here in Georgia.

      1. James - Post author

        WOO HOO! Another success story!
        (I grew up in Atlanta. You’ll want that extra-cold AC…)

    19. Liz

      Thanks for this great idea and explanation!. I ended up not having to do this to my air conditioner, however I am curious to see if you think you can add a wall thermostat to a non ducted dometic air conditioner. Got any ideas on that?

      1. James - Post author

        Well, I think it might be possible, but there would be new parts to order.
        Most of the manufacturers make a “ducted” ceiling box assembly – that assembly won’t have controls, and will have the ability to plug in remote controls.
        So yes, I think it’s possible. Worth it? I can’t say.

        1. Jon Roback

          Unrelated, BUT; Do you think I should keep my advent ac135 (similar unit to yours) on Low w/temp. On med.) (in Vegas at 120°F outside) or High with temp. Lower?

        2. James - Post author

          The only danger I’m aware of with air conditioners is the mythological danger of them freezing up. I’ve never seen it, but people say it happens. (People also say they’ve seen the Loch Ness Monster.)
          Anyway, in theory, freezing up an air conditioner would require moisture in the air.
          If you’re in Vegas… I’m pretty sure moisture in the air isn’t a concern.
          In your situation, I’d crank it. Max cool. Max fan.

        3. Brian R

          Thanks for info. Sounds exactly what my AC is doing. Not cooling trailer to below around 80. Not comfy at all. I will do what you did and let you know if it takes care of my problem. For a compressor to freeze up it has to be set real low. 60s

    20. David Reed

      Hey James,
      This is just what I was looking for. I have the same exact unit that you do. I have another question. Mine has a heat pump and this is used in my Sprinter Van so no furnace. My unit will not even come on at 42 degrees and below. Most people I have asked, have no idea because they have a furnace and they do not turn the unit on when it is below 42. Of course, I am trying to use the heat pump. Do you know of anyway bypassing this 42 degree system shutdown? Thanks David

      1. James - Post author

        I wouldn’t mess with the low set point of the heat pump.
        They just don’t work below certain temperatures.
        42 seems a little high, but I don’t know what the right set point would be.

      2. Vance Tietz

        James, I purchased a used Coleman Mach 3 13,500 with a new Coleman inner unit assembly (fan & thermostat controls). Installed assembly….the blower is working but the system is not cooling (70 degrees @ discharge (I don’t believe the compressor is cycling)). The outer unit appears to be in good shape & clean (no signs of leaks). The previous owner stated it worked good but, he replaced with a larger unit. Now, I may be creating my own issue…… outside temp was in mid 60’s when I was installing/ testing the unit. Does the outside temp have to be a certain degrees before the system will actually start cycling (to prevent possible freeze up)?

        1. James - Post author

          I don’t know about that, but I sort of doubt it. If that were the case, they never would freeze up unless that protection was broken.
          Sounds like a call to an RV Service Center might be in order.

    21. Chuck

      I just installed a dometic and it was not getting cold., Pulled mine apart like you showed and went 1.5 turn clockwise and was fine til i put the cover back on… I had to bend the actual thermostat away from the plastic and more out to the intake… Now its working perfectly…. So those 2 issues fixed it…

    22. Bobby G

      On my class


      When running my AC’s, I put the fans on manual speed, normally at med. and the compressor is the only item that cycles. This takes start up load off the gen set. And keeps the ac from ever freezing up. I normally keep my thermostats at 70 degrees.

      1. mike Beder

        My dometic is throwing an e 4 code Rich’s outdoor air temperature sensor I can’t seem to locate it in the air conditioner any suggestions

    23. Art

      My AC (Coleman Mach III 13.5) will kick on, begin to cool but after 30sec to a min or so, stop cooling but fan will blow. Generator nor breaker tripped. Temp outside & inside upper 80’s – 90ish. Then have to play with wall t-stat to get it to kick back on. Then happens all over again. Thoughts?

      1. James - Post author

        It certainly sounds like a thermostat issue. But as we don’t have a wall thermostat, I’m at a loss to tell you how to troubleshoot.
        In your place, I’d probably install a similar thermostat temporarily and see if that fixed it. Maybe a friend with the same model? Or buy a new one from a parts dealer?

    24. Smokeydog

      My original dometic AC on 94 airstream was great. We live in the south. The control board fried after 15 years. The cooling fins on the condenser were corroding off from being on the beach so wasn’t worth fixing. As a temporary fix I straight wired the unit to come on high only at max cool. Used a small ceramic heater as the thermostat control. This temp fix worked great for 6 years. Had the dealer install a brand new one. It sucks! Always freezes up and never gets cold. It doesn’t have a freeze sensor. Several dealers and call to Dometic confirm it is oporating as designed. Bad design! Suffered and cussed for 3 years. Installed a percentage timer switch between the thermostat and compressor to defrost. Adjusted the thermostat per your instructions. Got my cool happy camper back! External adjustable timer is mounted on ceiling next to ac. Setting on 93% at 15 minute cycle.

      It’s an engineer thing.
      Happy camping.

      1. James - Post author

        Glad you’re cool and happy again!
        I’ve heard that from several folks… that the newer air conditioner units simply don’t work as well as older ones. Some blame more environmentally-friendly designs and refrigerants.
        There may be something to that, but I’ve not seen an official statement from any AC maker to that effect.

    25. Joni

      Hey there! Our camper wasn’t blowing cold air this morning. It was also making a humming/buzzing noise that goes on and off while it’s on. We are definitely in humid weather so don’t think that it’s freezing up. What do you think could be wrong with it?

      1. James - Post author

        Several questions needed to get started on this one.
        What brand and model is your air conditioner?
        Is there no air at all blowing (fan issue), or is there air blowing, but it’s just not cold (compressor issue).
        If you let the unit sit idle for a whole day, will it then start up?

    26. Todd Piper

      I found all of this info interesting. Basically the air coming out of my RV AC is no where near as cols as the air coming out of my home or automobile AC. I assumed this was a low on freion issue. My RV is ionly 3 years old. I have a wall thermostat, could it just be low on freon or do you think it could be the same issue you identified with the internal AC aetting?

      1. James - Post author

        I would guess the problem is NOT low freon, but instead the internal thermostat setting discussed in this post.
        Just a guess, but I think regardless of what your wall thermostat says, an internal regulator on your AC unit will only let it get so cold.
        It’s simple enough to check, and could save you a trip to the service center.

        1. Chris Evers

          I have a wall thermostat and my Coleman 13500 is blowing cool air but not very cold. It never cools my camper down unless it’s at night. can I adjust the factory settings anywhere on my ac unit to make it blow colder? Thanks

        2. James - Post author

          I’d try to get the installer’s manual for the thermostat and see if there was a temperature bias or something like that.

    27. vocalpatriot

      “Back in the 1600s, they had air conditioners that froze up.”
      I remember that!!! We called it winter.

    28. Jim

      James, we have a thermostat controlled AC in our 5th wheel, but seem to have the same problem you did…it won’t ever get below 77 deg unless it is lower than that outside. Even when it is only 82-84 outside in SoCal, 77 is the lowest it will go. What do you think I should look for in our unit, Coleman Mach 15? I’m assuming to trace the thermostat wires into the unit and find something similar?

      1. James - Post author

        Hmmm… That depends on if the limiting factor is in the programming of the thermostat itself, or somewhere up in the AC unit.
        I’d say your guess is as good as any. If you’re feeling adventurous, go for it.
        One thing you might try is to get a wiring diagram for the wall thermostat, and then look for the wires that should be connected or grounded when the wall thermostat is calling for cooling. Then connect or ground those as appropriate (effectively bypassing the wall thermostat), and see if the air conditioning gets colder than 77. If it does, then you know the problem is in the wall thermostat. If it doesn’t, then you know that there is something in the AC unit itself that is preventing it from working properly.

      2. John smith

        I have a roof top unit with thermstat control on wall. When unit cools down an shuts off , problem begins when trys to come back on. It will click , click again come on, shut off and repeats until i turn thermostat down colder or run on manual

    29. Other Steph

      As someone currently living in Maryland with 92% humidity today… I can relate. I cannot wait to move back west in a few years!

    30. Michael

      LOL, that you mention Utah and not freezing up together. The only time I have seen bigfoot, I mean had my AC freeze up, is in Moab, Utah. I swear it was 110 during the day and still 85 at night and it never went off. Took cover off and it was one solid block. Drove out of the park and to the McD’s let it sit in the sun and melt while we sat inside.

      1. James - Post author

        We’ve camped in Moab plenty of times and never had an issue like that.
        If your air conditioner freezes up in Utah, I’d bet there were other problems at work.

    31. Jonathan Miller

      Thanks for the tip, but I can tell you your 62F limit is not chiseled in stone. Here in Houston where the humidity is often un triple digits I have frozen up my AC when the temperature is in the upper 70s. I try to get my coach as cold as possible at night to coast through the next day, but a couple of times I froze it up and I can guarantee the outdoor temperature never dropped below 78F

      1. James - Post author

        Well, it sounds like you might be one of those who needs to do his own testing to determine an appropriate limit. But… if my AC was freezing up at 78 degrees, I’d be looking for a different problem (low freon, etc) or replacing the unit altogether.

      1. Becky glenn

        Have roof top carrier aircondition air comes out cold but kicks off and on then air gets hot any ideals on what to do .

    32. Aaron

      Are you still planning to run the AC full blast when you travel to more humid parts of the country? We’ll likely be in SLC again next June. This quick mod will be on the top of my list for that trip.

      1. James - Post author

        Yes, I do plan on running this way regardless of location – but not below 62 degrees outside.

        (Although, to be honest, my desire to visit someplace is pretty much inversely proportional to its relative humidity…)


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