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Separate Furnace & Air Cond - 1 Ecobee3 Thermostat

My goal is to control two separate systems with one Ecobee3 thermostat for my church. The furnaces are at one end of the sanctuary and the ac units at the other. Previously, they used separate thermostats. Both system have their own blower fans. There are no sample drawings of this application shown in the Installation Instructions. I'm using Rc and Rh as both systems have their own transformers. The ac system is two stage. Right now there are two furnaces that are "twined" and operate as one but I may stage them at a later date.

The furnaces worked great all winter without the ac system connected. After I ran the thermostat wiring across the building to the thermostat and connected the ac and the Ecobee, only the first stage of the ac was working. I went into system settings and saw that only one stage was shown for the ac. When I attempted to change that, the thermostat went into self configuration mode and is now stuck reporting an error in configuration wiring.

I don't know which system should connect to "G" for the fan. I'm using the "G" connection for the furnaces blowers right now. I tied the blower fan relay for the ac to Y1 so it will run whenever there is a call for cooling, Y2 goes to the 2nd stage ac unit. Is that causing the configuration error?

I saw Spence offered to draw a wiring diagram for a previous poster with a problem close to this (but not close enough to work in this configuration).


    HVACNUT Member Posts: 5,251
    I'm not familiar with the Ecobee but there should be an option for heat, fan controlled by thermostat, or fan controlled by equipment. It should be set to equipment. Both systems cannot connect to G.
  • GBart
    GBart Member Posts: 746
    RC, Y1, Y2, G cooling
    RH W heating

    might be too late, Ecobee should have technical support
  • Moonwink
    Moonwink Member Posts: 7
    edited June 2018
    I worked with it some more yesterday. Finally made some progress after I tried removing all the wires for the a/c and let it configure itself. When it asked if it had the right configuration, I changed it to say the furnace fan should be controlled by the furnace, the Rc was connected, the Y1 & Y2 were connected. It accepted that configuration and began working again but even set 10 degrees below the ambient, the second a/c wouldn't come in. I rechecked the system settings and gave up connecting the a/c fan, stage 1 and stage 2 to Y1. It works and cools. I just hope there's not too much power draw on Y1.

    I never found any setting to show when Y2 should come in but surely it should be active when the set point is 2 degrees lower than the room temperature and that's not the case here. The snowflake shows a 1 next to it. I never could get it to show a 2.

    I've sent an email to Ecobee asking for their support before I posted here.
    HVACNUT Member Posts: 5,251
    Check the wiring at the condenser. I've seen many a Bozo splice both stages together.
  • Moonwink
    Moonwink Member Posts: 7
    Thanks but, it's easy to tell when the 2nd condenser is running. The liquid line gets warm and the room begins to actually cool off. If I hadn't tied Y1 and Y2 together, the 2nd stage unit wouldn't run.
    HVACNUT Member Posts: 5,251
    I didn't know you did the control wiring so I apologize for the Bozo comment.
    If I understand correctly, the 2nd stage runs if you connect it to Y1 at the thermostat? And when the 2nd stage wire is connected, the Ecobee can now "see" Y2 is connected?
    Can you post pics of the schematics for the condenser and A/H? Is there an ambient or time delay control at the condenser?
  • Moonwink
    Moonwink Member Posts: 7
    The system is 30+ years old. The 2 air handlers are horizontal Friedrich models and the 2 condensers are Lennox. They're 5ton/3phase each. Very simple wiring - fan relays in the air handlers are tied together, contactors for the condensers are separate providing for staging. I previously used a 7 day thermostat for the a/c system and the 2nd stage would come in as needed. Since combining the furnaces and air conditioners on the one Ecobee, the 2nd stage ac doesn't run even when the setpoint is 10 degrees below room temperature and only the snowflake and the number 1 where showing after several minutes of running. That's when I tied the 2nd stage to the 1st along with the fan.

    Haven't seen a reply to the email I sent to Ecobee Support.
  • ratio
    ratio Member Posts: 3,502
    How long did you wait for second stage to come in? While I would expect 10° from setpoint to immediately stage up, but sometimes software guys are too clever for the rest of us.
    HVACNUT Member Posts: 5,251
    Ok, I thought you had as typo in a previous post. You're dealing with a furnace and 2 A/C systems. One for 1st stage, one for 2nd stage.
    A lot of older split systems had the transformer in the condenser.
    Are you dealing with 3 transformers total, or 2?
    Rh-W is figured out for the twinned furnaces.
    On the A/C systems are you using 1 transformer to control the fans and both condenders?
    220v primary, 24v secondary?
    What's the VA rating on the transformer?
  • Moonwink
    Moonwink Member Posts: 7
    2 transformers. One for the furnaces and one for the air conditioners. The air conditioners share a transformer in one of the air handlers. All it has to do is power a couple of fan relays and the two contactors in the condensing units. Yes, it is 220v primary and 24v secondary.
    I'll admit, I haven't looked at the VA rating. My answer will have to wait till tomorrow when I get over there again. It's been working with the same transformer and relays for over 30 years - maybe closer to 45 years. I think the old timers said they installed the air conditioners in the 60s - they don't get used much. They are approaching end of life due to rust eating up the condensate pan but I would replace them with like items and retain the same configuration. No budget for anything else.
  • Moonwink
    Moonwink Member Posts: 7
    I waited close to 10 minutes for the second stage to come in. Even after I combined everything, I never have seen the "2" light come on.
    HVACNUT Member Posts: 5,251
    Ecobee should have a toll free tech support number. He might be risen by the time they respond to email.
  • Moonwink
    Moonwink Member Posts: 7
    edited June 2018
    Ecobee's Reply Answers the Questions I Asked:
    (Very Helpful! - I incorrectly used the "C" common wire from the furnace)

    The G fan in a dual stage transformer system would need to come from the cooling system as the RC would be used to garner the power for that portion of the system. A blower fan would be automatically energized for a furnace and the G wire is usually used for the compressor cold air to be pushed through the vents.

    From the A/C side the wires that should be connected are:
    G (The fan wire from the A/C side would be connected here)
    Y2 (Your second stage of cooling wire would connect here)

    From the Furnace the wiring should be as follows for the thermostat:
    The G wire from the furnace would not be needed as most furnaces energize the fan by themselves. You would not need to connect this to anything

    When you do the reconfigure make sure that you change the "fan energize by" to the furnace as if you do not the fan for the compressor will be energized and turn on for calls for heating.

    If you have any other questions do not hesitate to answer this email or call us 18779326233 and refer to ticket number XXXXXX for more assistance.

    Happy to help
    ecobee support
  • Jamie Hall
    Jamie Hall Member Posts: 21,528
    Nice to see a company stepping up to the plate like that.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England