Forum Discussion

otrfun's avatar
otrfun
Explorer II
Apr 05, 2014

High Efficiency 13.5k BTU a/c = Smaller Generator?

Here' some specs (BTU/Compressor Amps/Fan Amps/Inrush-LRA):

Dometic (standard unit) 13,500/12.4/2.5/63
Total amps: 14.9

Colman Mach (standard unit) 13,500/11.9/3.4/63
Total amps: 15.3

Dometic High Efficiency 13,500/8.6/2.5/50
Total amps: 11.1

Coleman Mach 3 PS 13,500/8.3/2.9/58.4
Total amps: 11.2

Once started these high efficiency units use about 3-4 amps less current than the standard units. The Dometic has a respectable 13 amp (63 to 50) reduction in inrush/LRA/startup current. A very good thing for smaller generators.

Did notice the Coleman Mach 3 PS had much less reduction in inrush/LRA/startup current vs. their standard unit. Wonder why? Quite a few small generators will never have the opportunity to see the reduced steady current demands because they'll never get the past the higher inrush/LRA/startup current.

Typically these high efficiency units can be purchased for $650-$750. Purchasing one of these might be a better investment vs. buying a larger generator--say, one EU2000 vs. two EU2000i's--$1000 vs. $2100 :)
  • TurnThePage's avatar
    TurnThePage
    Explorer
    Apr 05, 2014
    Do they use a hard start cap? That significantly reduced the initial amperage load on my Coleman MachIII.
  • otrfun's avatar
    otrfun
    Explorer II
    Apr 05, 2014
    BillyW wrote:
    Do they use a hard start cap? That significantly reduced the initial amperage load on my Coleman MachIII.
    That's a good question. These specs were pulled from aftermarket literature. I'm assuming these specs reflect use of a starter caps; however, I can't be certain.
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    Apr 05, 2014
    Carrier Air V (no longer made) 13.500 BTU 13.5 amps

    Advent Air (Replaces top (Roof) unit on the Carrier when the Carrier fails due to poor construction) 15000 BTU, 13.5 amps.

    (My Front and Bedroom air conditioners,,respectively)
    (Construction fault corrected on front unit...By me).
  • dougrainer's avatar
    dougrainer
    Nomad
    Apr 05, 2014
    Dometic does not offer a Hard Start Cap on regular units. I am not aware of Dometic offering a Hard Start Cap as a optional part.
    RVP DOES allow you to option a Hard Start Cap. BUT, that may be OEM only and you have to purchase the Hard Start Cap kit from RVP. When you talk to whoever you are buying from, ask for the Hard Start CAP system. That will usually be a Special order, so it is quicker to just buy the RVP model you want and buy the RVP Hard Start Cap as an extra part.
    If you read the archives, you will find a lot of RV'ers using a non RV Genset having good luck with adding a Hard Start kit. You do NOT have to use the RVP Hard Start kit. You can get one locally from your regular HVAC supply company. Doug
  • dougrainer's avatar
    dougrainer
    Nomad
    Apr 05, 2014
    otrfun wrote:
    dougrainer wrote:
    Dometic does not offer a Hard Start Cap on regular units. I am not aware of Dometic offering a Hard Start Cap as a optional part . . .
    When you say "regular" do you mean OEM or aftermarket?

    Dometic #3310727.015 Hard-Start Kit

    Dometic #3102903.006 Hard-Start Kit


    AS OEM build, not buying the AC with the Hard Start kit installed. Thank you for the link. The RVP model number tells you if the RVP has the Hard Start kit already installed by RVP, but I have that info at work about what part of the model number tells you that. Motorhomes usually do NOT have the RVP hard start kit as the APU's motorhomes have are RV designed APU's and have no problem starting the AC unit. Towables that have NO APU from the factory sometimes have RVP optioned Hard Start kits because the OEM realizes that RVer's may use smaller portable APU's that need the extra boost the Hard Start kit supplies. Doug
  • pnichols's avatar
    pnichols
    Explorer II
    Apr 05, 2014
    I'm curious, why would one NOT want the Dometic High Efficiency unit on an RV they were going purchase or replace the A/C on (if they had a choice) ... regardless of generator power considerations? At the very least, more efficent operation means less generator fuel consumption when using the A/C when not on hookups.

    Also, if not concerned with generator fuel consumption during A/C use ... I wonder if a high efficiency 15K unit exists, and if it does ... why not put/order the 15K unit on an appropriately sized size RV instead of the 13.5k unit that might normally be adequate for it? A high efficiency 15K unit might have about the same current ratings as a standard efficiency 13.5K A/C. An extra margin of cooling capacity just might be useful at times. We have camped in un-anticipated conditions with our small Class C motorhome where it's 13.5K A/C unit could barely keep the rig comfortable and a 15K A/C unit really would have been the ticket.
  • time2roll's avatar
    time2roll
    Nomad
    Apr 05, 2014
    Yes and unfortunately the fan starts before or the same time as the compressor.
    When will they figure out it is ok to run the compressor ten seconds before the fan kicks on.

    Or has this changed? I installed a new Dometic control box/digital thermostat a year ago and it starts the blower fan first by design.
  • otrfun's avatar
    otrfun
    Explorer II
    Apr 05, 2014
    smkettner wrote:
    Yes and unfortunately the fan starts before or the same time as the compressor.
    When will they figure out it is ok to run the compressor ten seconds before the fan kicks on.

    Or has this changed? I installed a new Dometic control box/digital thermostat a year ago and it starts the blower fan first by design.
    Can this Dometic digital thermostat be used on the garden-variety, Dometic 13,500 BTU, non-ducted, rooftop units? Got a part number? All the units I've seen, the fan runs constantly, 24/7. It would be awesome to have the fan turn off with the compressor.

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