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tom496's avatar
tom496
Explorer
Apr 14, 2013

Need help with Air Conditioner / Hard Start Capacitor issue

Our 2005 TT has a Dometic Duo-Therm 13,500 BTU ducted A/C, model #57915.331. Last year, I picked up a used Yamaha 2400IS (not ISHC). I got the generator mainly for recharging the batteries and for occasionally running the A/C while dry camping.

In my initial attempts to run the A/C off the generator, the generator was going into overload about half the time when I switched on the A/C (compressor and fan together). By starting the fan first, I could get it running most of the time, but with significant strain on the generator. This was in 70 degree weather in St. Louis (low elevation) with the converter unplugged and refrigerator off. This made me pessimistic about running the A/C in summer temperatures or at any elevation.

I decided to install a Supco SPP6E.

Here's what I found in the capacitor box on the A/C:


I removed the existing starting capacitor:


I connected the SPP6E wires to the same spades on the run capacitor that the starting capacitor had been connected to, as shown here:


There was no noticeable difference in starting performance.

After some more research, including reading the lengthy threads on this topic on ModMyRv.com here and here, I decided to try either a SPP6 or SPP4E.

I ordered a SPP6 on Ebay. It arrived yesterday and with it installed in place of the SPP6, it is even more difficult to get the A/C started (again, cool day with the converter unplugged and everything turned off). Even when I fire up the fan first, I cannot get the compressor running before the generator pops the breaker.

I realize that others have been unable to get a similar A/C to operate with a Yamaha 2400IS, but it seems like they’re in the minority.

The A/C is clean and the fan spins freely. It has never tripped the 20 amp circuit breaker the TT is plugged into using about 20 yards of extension cord at home. It did seem today as if, on house power, the compressor hummed for several long seconds before the compressor fully started up, which I had not noticed in the past.

I’m not ready to give up on this yet. It seems like the Supco SPP6 could be bad, and there may be an issue with the A/C or the generator. I would appreciate any suggestions, including ideas on an approach to troubleshooting or analyzing the situation. I have a Kill A Watt and a digital multimeter. I’m willing to pick up a clamp-on ammeter if it might yield any useful data. Thanks in advance for any help.

10 Replies

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  • Chinolbz's avatar
    Chinolbz
    Explorer
    Jun 08, 2013
    The Yamaha 2400 is a great unit but would not start my 13.5 AC. Chino
  • bob213's avatar
    bob213
    Explorer
    Apr 15, 2013
    According to an email response from Supco, the SPP6 is the correct capacitor for your needs. If you don't have a stand alone start capacitor you "piggyback" to the run capacitor. You installed your's correctly by replacing the existing with the new SPP6. As ktmrfs mentioned you can get a fan delay that might help. I use two Honda 2000's so I have no problem starting. I cannot comment on the ability of the Yamaha 2400.

    Here's a link for a delay timer...
    Delay Timer
  • rkentzel's avatar
    rkentzel
    Explorer
    Apr 15, 2013
    I doubt your hard start is bad. I would check your run load amps, check the capacitance of the dual run cap make sure its up to snuff. You may have a compressor going out on you. You can also ohm out compressor terminals.
  • TRIPLE8's avatar
    TRIPLE8
    Explorer
    Apr 15, 2013
    Hi, I cannot help you with your capacitor, what size ext. cord are you using? You should be using one rated for at least 15 amps.
  • ktmrfs's avatar
    ktmrfs
    Explorer II
    Apr 15, 2013
    since the AC already had a starting cap, I wouldn't expect much improvement from the supco. AC units w/o a starting cap (most of the coleman Mach III OEM's BTW) benefit the most.

    I'll agree with Wayne D., the dometic you have seems to have a reputation of one of the easiest to start units and best luck with Honda 2000. Are you sure ALL the other loads in the trailer are off when the AC starts? (That includes the converter, fridge on AC etc.) Even with the yamaha, your in somewhat marginal territory with additional loads until the compressor motor spins up and is drawing normal current. But the yamaha should be in the "barely adequate" category, rather than the "almost adequate" category.

    And if you can control the fan startup, it's better to have it start AFTER the compressor has started rather than before. that way there is less load when the compressor starts. On my AC I have a 10 second delay between compressor start and fan start. Fan draw isn't much, but every amp hurts during startup. The worst thing is to have both motors trying to start at the same time, although the fan will spin up quickly since it really isn't loaded much.
  • PaulJ2's avatar
    PaulJ2
    Explorer
    Apr 14, 2013
    Without getting into heavy duty theory here--starting capacitor sizes are picked to function with a certain motor depending on the internal resintence of the starting windings,it's wire size and etc, etc. So too much capacitence is as bad as too little.
    So adding the capacitor is probably taking it too far from it's
    optimum value.

    I also don't see the PTC motor starting device in your second picture. This needs to be in the circuit also.
  • Wayne_Dohnal's avatar
    Wayne_Dohnal
    Explorer
    Apr 14, 2013
    Without good electrical measurements or swapping components everything is opinion. Mine is that there's something wrong with your generator, air conditioner, the interconnections, or you have an additional AC load you aren't aware of. I base my opinion on (1) My eu2000i started a 57915 with 100% reliability on 90+ days, and (2) It will start my current 15,000 btuh unit at at 70+ degrees and 3,500 feet, (3) Compared to the eu2000i, the 2400 VA Yamaha is "over engined", so I'd expect it to do better than a straight 20% improvement over the eu2000i.
  • tvman44's avatar
    tvman44
    Explorer
    Apr 14, 2013
    The Suppco is supposed to be added in parallel to the original cap. If you remove the original you are no better off than before.
  • Altern's avatar
    Altern
    Explorer
    Apr 14, 2013
    With all due respect, IMHO you should find someone who knows about such things. Please start with a technician making a living at servicing HVAC equipment. Good luck.

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