Installing Hard Start Capacitor into my RV Air Conditioner

Why do I want a Hard Start Capacitor?

When dry camping there are times I would like to run the roof-top air conditioner to cool the camper down. I have a pair of Champion 2000w inverter type generators that I can parallel together for 4000 peak watts and 3200 continuous watts of power. They normally can power the AC fine except when the temps and humidity climb and it gets really hot, like above 95F.  In these conditions, the AC’s compressor needs more current to start and will cause even the two paralleled generators to overload, especially if we have a few other things running and also drawing some current in the trailer.

While researching a solution, I came upon many forum threads and blog posts expounding the virtues of installing a hard start capacitor kit. Researching it a little more I discovered my RV’s roof-top air conditioner didn’t have the hard start kit, but one could be easily installed. I decided to get a hold of the hard start kit and give it a whirl.

Hard Start Capacitor HS6

Hard Start Capacitor HS6

What Model AC do I have?

My Keystone Cougar 276RLSWE Fifth Wheel trailer came equipped with an AirXcel 48203A866 Air Conditioning system utilizing the Coleman Mach III rooftop AC unit. The particular model installed does not have the optional hard start kit. If you look at the schematic (photo below) from my units sheet metal cover you can see the dotted lines where it can be installed.

Schematic Diagram   AirXcel Specs

Where did I get the hard start kit?

Seeing that my unit can utilize a hard start kit which consists of an electrolytic capacitor and a PTCR device plus hook-up wires I searched around for one. Not having much luck with local stores and being in Canada ordering from the US can be a pain. I picked one up off a supplier on EBay for around 15 bucks including shipping. One of the mysteries of modern trade, stuff gets shipped easier and cheaper from China to Canada than right next door in the US. *shrug*.  If you’re in the US you can order the part off Amazon for a similar price.

Supco SPP6 Hard Start Kit
Price: $14.40
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18 new from $8.920 used

What is a PTCR?

Great question, a PTCR stands for Positive Temperature Coefficient Resistor. Here is a link to a full explanation but the main thing it does in the circuit is to allow a boost of current to the compressor when it first starts up and then the PTCR heats up and changes it’s resistance to close off the extra current because it is no longer required. The compressor only needs that extra juice to get started, after that the stock run capacitor is plenty and having too much boost can overheat the compressor. There is another style hard start kit which uses a relay instead of a PCTR to accomplish the task, but I chose the PTCR device type because that is what is included in AirXcel’s OEM hard start kit.

View of PTCR device

View of PTCR device

How did I install it?

The research and finding the right part was the hard part. Installing the hard start capacitor into my RV air conditioner was super easy! All you need is a Philips screwdriver and the ability to get up on the RV’s roof. I also used a couple of zip ties and a few dollops of clear silicone adhesive. First, remove the plastic protective cover to expose the air conditioner.

On the driver’s side of the AC, there is a small access panel with a few screws. Once you get that off you will see a bunch of colored wires and some capacitors. On the inside of the access panel, you should find a schematic, look for the run capacitor. That is the capacitor the hard start capacitor will connect to. The wire on the hard start capacitor connected to the PTCR goes to the same connector as the red wire and the other wire goes to the yellow one.

The connectors should just clip on to some extra lugs on the run capacitor. After you get the electrical connection completed then all that is left is to mount the hard start capacitor. I decide on mine to use clear silicone adhesive to hold the capacitor in place and did up the wires with a few zip ties.

 Electrical shock hazard! Before working on the AC unit make sure all power to it is disconnected.

Coleman Mach III AC opened up

Coleman Mach III AC opened up

Run Capacitor Location  Hard Start Cap Installed

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Installing Hard Start Capacitor into my RV Air Conditioner Video

Did it make a difference?

It’s hard to say early on. The compressor does sound like it is starting a little easier. To really know I’m going to have to be in a very hot humid environment where the compressor draws its max current on my pair of Champion Generators and see how they perform. I plan on doing some tests and update this article with my findings. First I want to see if now I can get the AC to run with only one of the 2000w generators without it overloading. I could never do that before, not surprisingly as the minimum amperage my model of AC calls for is 18.6 amps which is right near the 2000 watt surge capacity and way above the 1600 watts continuous capacity of my Champions. Even if it does run it won’t really be practical to use it but it’s a good test.

I guess having the hard start kit will help the AC run a little easier in those RV Parks with sketchy electrical prone to low voltage. I read low voltage can be hard on the compressor and even damage it and is one of the reasons listed to install the kit. If you have a generator that is running your AirXcel 13,000 BTU AC but prone to overloading easily it might be worth looking into installing the hard start kit. I’ve read about guys having good luck running 2000w to 2400w generators that would not work properly prior to the install.

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    I stumbled upon this topic trying to use my wife’s old makeup air compressor as a tire inflator
    it has a refrigerant compressor that tops out at 140 with no trouble, it draws 2 amps when running by the killawatt (find those at harbor freight ) but its instantaneous demand of
    77 amps to start up just kills my coleman 1850, once or twice it started and ran fine
    so i’m down to a starting cap.
    It seems that this is a ubiquitous problem for refrigerant air compressors, engineering expectations is that the units will plug into street power and high starting current is
    not considered.
    P.S. I braised a fitting onto the intake to vac down my A/C too
    Ill let you know if the whole thing works out

    Bill and carol
    40 foot schooner
    38 coachman
    19 santa maria
    and I was looking at a trans van to drop a dodge diesel in
    I work really hard at retiring!

  • Ron Alexander Sr.

    Also look into a soft start kit. Might be more expensive but this is the ‘conventional’ solution to minimize high start up current. If you use a soft start kit and your generator is sized for the run wattage then you do not need a second generator to handle the start up load.

    • How much are they? Do you have a link to one. Thanks Ray

  • Malakie

    I have a question.. Front AC compressor was not kicking in.. Thus either the start cap is bad or the compressor died. Went with a start cap to begin with for obvious reasons. Installed it. Turned the unit on and the cap blew up.

    I know electronics but AC units are not my expertise… However I am assuming that installing the new cap and having it literally blow means the compressor is definitely toast … (cap blew because WAY too much power was being pulled through it trying to start the compressor).

    Is this a correct assumption? And if so, anyone know where I can get a salvaged, used, cheap replacement Coleman Mach III ac unit for my RV?

  • Erick Sill

    Wow !!! I found this forum the other day. It was just what I was looking for. I have a Coleman Mach 3 on my travel trailer. Here in Calif when we dry camp we occasionally need A/C and my Yamaha EF3000iseb didn’t have enough power to start the compressor without overloading the generator. Yesterday I went to my local A/C supply house and bought the matching Hardstart capacitor, installed it in about 10 minutes and now my Yamaha generator starts and runs my A/C unit immediately with ease. The ambient temp was about 85 degrees, on startup the temp at the A/C duct vent was 81.4 degrees, within 3 minutes of running it measured 76.1 degrees. Needless to say I’m very pleased, thanks for a great video and the followup posts.

    • Awesome! Thanks for taking the time and leaving a comment. Cheers Ray

  • Ray Whyte

    Ray, what were the results of you install, Did it do what you wanted it to do? Can you run the AC on one champion generator?

    • No , it won’t quite do it on one Champion, they say 2000W but in reality they are only a 1600 watt continuous machine. The newer ones may do better as I think they have newer firmware and a little more power.
      The pair of Champions parallel has no problems though.

  • Grant Madison

    Ray – a question re your hard start cap installation.

    From your pics and wiring diagram, it looks like your A/C unit did ‘come with’ (‘already’) (a) dual, separate start and run caps, yet you said that it did not have a ‘hard start kit’. (I GUESS? that means that it’s the ‘Capacity’ (in microfarads) of the ‘start cap’ which determines whether it deserves to be call (a) ‘hard start’ (kit)/capacitor???

    ANYWAY: I was just wondering/wanted to confirm my IMPRESSION that you installed your new HS6 cap ‘in parallel with (i.e. did not disable and/or remove) the ORIGINAL start cap. CORRECT???

    FYI: I was ‘one the phone’ with a Supco rep last week for about 10 minutes and during that conversation I asked him *IF* one was supposed to disable the original start cap and install the SPP6 in its place OR install the SPP6 ‘in parallel’, and his response was to INSTALL IT IN PARALLEL. (Right now, my original start cap is disabled).

    Also FYI: the Folks at Supco were quite nice and responsive. I got a (response) phone call from them in less than 1/2 hour after I sent them an email with a bunch of questions. Got several answers and, again, quite pleasently, the rep I was talking with extended an offer (which I accepted) to have a MUCH MORE TECHNICAL guy, on vacation this week, call me next week so that I could discuss things more with him.

    Soooo… If you have any questions you might wish answered, pass them along and I will ask.

    BTW: In response to my questions, I was told that, in addition to ‘leave the stock start cap in place’, that (a) the SPP6 ***WAS*** ‘THE’ best cap to use (NOT the SPP6E; though many people do) and (b) that ‘polarity’ (defined here as which wire one connects to ‘red’, etc. did not matter (SEEMS to make sense to me).

    He went on to say that ‘they’ (at Supco) were quite surprised at the surging interest by RVers in ‘start caps’ to enable them to (hopefully) have more success at firing up A/C units without having to have ‘Big Generator’ capabilities.

    Again, if you have any questions, pass them along.

    • Hi Grant, Mine only had a run and fan capacitor, the start cap is an optional kit. I used the AC manufactures own PDF on Hard Start Kits as my guide – You can see in the bottom diagram how the optional start components are wired in parallel with run capacitor.

  • SuperDad01

    I noticed that Supco also makes a SPP7 and an SPP8. Would they work better and offer more starting assistance?

    Or is the SPP6 the only one that should be used on a Coleman Mach III RV air conditioner?

    Any suggestions on where to get a replacement for the starting capacitor that came with the RV A/C? If the cost is not too high I think I will replace it while I am up on the RV roof installing the hard start kit.

    Thank you.

    • Sorry SuperDad, not sure on that, if you find out please post a reply and let me know, thanks Ray

      • SuperDad01

        Hello Ray,

        I found the Supco website and they have a very nice document with more information about hard start devices than the average person would care to know. The document can be found here:

        On the last page they have a chart that shows the recommended part numbers for air conditioners with capillary tubes or fixed restrictors, which are the type used in RV air conditioners.

        Supco recommends part number:

        SPP5 for 300% more starting torque

        SPP6 for 500% more starting torque

        SPP7s for 600% more starting torque

        These are all Positive Temperature Coefficient (PTC) type hard start devices.

        Thanks for writing a great article.


    • Thanks for the PDF link, interesting stuff.

  • Mama

    I went to a motor repair guy and bought my capacitors, and electrical supply houses might carry them, too. They aren’t “that” specialized. Be sure to match up the ohms and voltages. The shape of the capacitor might be different from what you take out. Except for the hard start capacitor, I bought it on eBay from one of the major RV suppliers. They are easy to find. Good idea to keep spares on hand in case they go out, too.

  • James

    I’m a little confused! My start capacitor is blown and doesnt work, hum comes from AC unit inside. Do I need another start capacitor + this hard start capacitor in order for the AC to work?

    I have started the fan by hand and got the unit running, but when I put it on low/high Cool setting, the unit ices up!!

    Any advice much appreciated!


    • This is just an optional add-on capacitor. If your start capacitor is blown you need to replace it with an OEM replacement capacitor. That will get your AC back working assuming no other components are defective.

      • James

        Thanks, can you recommend where I might be able to purchase one thats not to costly? I have a Gulfstream Travel Trailer. The Coleman unit model # is 83338876. Thanks again! James

        • The RVComfort site has the documents – if you look in the parts PDF they list the start capacitor as run capacitor. There is another one called fan capacitor, so make sure you get the right one. Lots of pdfs there with diagrams. Then do a web search for the part number + Coleman Mach should get some results. I found this page –
          Also maybe a local AC servicing shop may sell you the part. I’m sure they are common in house ac units as well. Cheers Ray

        • James

          Much appreciated Ray, will contact RVPlus

        • James

          Hey Ray, not sure if they know what going on at RVPlus, this was the response i got!! Not good doing business with with this company. Not even the question I asked them,
          oh well….. happy camping!!

          We do carry Coleman products but we don’t do any kind of servicing. For
          technical information you will need to contact Coleman directly. The number
          for their customer service department is 316-832-4357.


          name omitted!