Forum Discussion

pascoscout's avatar
pascoscout
Explorer
Dec 25, 2018

Connect Atwood AC-1351 to AGS

I recently received my new toy hauler that was custom built. One feature I wanted was to have the generator automatically start when the roof top AC unit comes on. To do this I had the installer put in a Xantrex SW 3012 inverter/charger and a Xantrex Auto Generator Start controller. What I expected to see was the AC unit to be powered via the main AC panel and a low volt connection from the AC unit on the roof to the AGS on one of it's thermostat trigger leads. After going through the electrical system what I have found is the installer wired the AC units to run through the inverter with no direct connection to the AGS. It's below freezing here now so it's not easy to test the AC but what I am assuming will happen is the AC will come on and then drain the battery down to a point the AGS fires up the generator. While this may work it really isn't what I wanted.

So after this long story what I am really after... has anyone been able to get a signal from the Atwood AC-1351 to trigger an AGS unit? The Atwood has an integrated control panel (may be able to be removed and wall mounted) that has 4 wires running to the units main board. My assumption is I would need to figure out which wires send the signal to fire up the compressor (or may just the fan since it would always be on if the compressor is on) and connect those to the AGS, which in turn would tell the generator to turn on. If anyone has done this I'd really appreciate some pointers. Thanks!
  • pascoscout's avatar
    pascoscout
    Explorer
    Jan 01, 2019
    Interesting idea. Will have to think that one through and see how I could make it work. I also need to test the AC unit on the inverter to see how bad the draw down really is.
  • H20ENG's avatar
    H20ENG
    Explorer
    Dec 31, 2018
    My DIY budget minded brain points me toward this solution. There may be a more elegant electronic solution but this would work:

    1.Rewire the ACs to 120V breakers and off the inverters.
    2.Depending on the input voltage needed by the AGS, use a relay tapped off the thermostat cool signal to trigger the AGS. Wire these parallel with each AC so either will start the gen.
    3.On said thermostat cool signal wire(s), run these through time delay relays to the AC units, so that the generator will be up to speed and transferred before trying to start the ACs. (3-5 min should be plenty)
  • pascoscout's avatar
    pascoscout
    Explorer
    Dec 27, 2018
    I agree that running the AC units through the inverter is not a great plan, hence why I am here trying to figure out a way to change it.

    The AGS has two sets of thermostat inputs labeled Thermostat input and return (1 & 2 respectively), neither of them have anything connected. The AC unit itself does not have any way to connect an AGS that I can see so they are probably not designed for it.

    I guess I'll have to see what kind of voltage is going through the wires connecting the control panel on the AC unit to it's main board. Will look at other low volt connections in the AC unit to see if there is anything I can try tapping into.

    One issue I can see is supplying the power to the AC unit when the generator is not on. I assume that AC units with an AGS lead have addressed this somehow, possibly by having 12v from the battery to the AC unit just to run the thermostat. Or does the AGS supply the power to the thermostat?

    I am not opposed to swapping AC units to get what I want but would like to exhaust this option first as that's a lot of money.
  • Chris_Bryant's avatar
    Chris_Bryant
    Explorer II
    Dec 26, 2018
    The only easy way is to use a separate thermostat wired to the AGS- you *might* be able to hack a sensor on the outside blower, which is single speed (inside blower is 3 speed).
    Or, you could buy an Onan EC-30W, which is designed to do that, but also uses a separate thermostat (built in to the device).
    Or, you could swap the Atwood units for Dometic CCC2 controlled models, which have AGS signal output.

    The only rigs I have seen with inverter run air conditioners were 24 volt inverters, with massive battery banks and oil cooled alternators to charge and run them, built on Prevost chassis.
  • dougrainer's avatar
    dougrainer
    Nomad
    Dec 26, 2018
    A 3000 watt Inverter is NOT DESIGNED to run 2 AC units. While the rating may indicate it, it is not designed to do that. I would NOT run ANY Roof AC on/thru an Inverter. NO NEED TOO, as the current draw will deplete the batteries in no time. The simplest way to determine HOW your AGS is wired is to go to the control module with the 20 pin quick connect. Check the AC tstat wires and see if they are used. If not used, then you do not have correct AC start. Doug
  • pascoscout's avatar
    pascoscout
    Explorer
    Dec 25, 2018
    Yes it's the Xantrex AGS. Have that, the inverter and the System Control Panel all wired with the Xanbus.

    The interver is rated high enough to run both AC units at once but it will likely deplete the batteries very quickly. May draw down too fast and shorten battery life as well. Main reason I want to change it is I want to be able to run the other inverter loads without worrying about exceeding the inverter capacity. With both AC untis on it's about 5 amps away from topping out.

    A temp sensor would be nice but if I can get the low volt singal to the AGS it will do effectively the same thing. The AC unit will send a signal to the AGS and fire up the generator. The way the manual says the AC unit works it the fan comes on first and the compressor fires up about 3 minutes later. Based on that I think I'll try and get the signal from the fan on, that way the generator has time to start before the compressor needs AC power. I suppose I could put in a thermostat that only connected to the AGS and then coordinate that temp setting with the control panel on the AC units. Would take a bit of guess and check but would work like your magnum does.

    Will try the heat gun option and see if I can get it to start. Was also looking at the unit again today and it has a "dry" setting which should cause the compressor to turn on to help dry the air. Was really hoping someone else had done this and could point me in the right direction.
  • dougrainer's avatar
    dougrainer
    Nomad
    Dec 25, 2018
    1. The AC units should NEVER be wired THRU the Inverter circuit. THAT is WRONG
    2. Is this the Xantrex AGS you have? Xanbus™ Automatic Generator Start (AGS)
    3. I prefer the Magnum system as the Magnum AGS module has a Temp sensor that you install in the Living area of the RV and THAT triggers the Genset to come ON and the AC units will be ON but without 120 until the Genset starts supplying power. No need to have to run the Interconnect wiring to your AC units like you have to do on the Xantrex BUS system.
    4. You can still test the system in your cold area. Use a Hair dryer or heat gun to warm up the tstat or tstat sensor to trigger the system. Doug

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