California Ecobee 4 with dxm2

Discussion in 'Maintenance and Troubleshooting' started by BLAKE STARR, Jun 15, 2018.


    BLAKE STARR New Member

    Hey guys,

    I just installed my climatemaster tranquility 22 heat pump and have everything working except the dehumidifier.

    With ecobee it shows that for a 1 line dehumidifier setup that the 24v line be plugged into the acc+ terminal at the ecobee.

    However, when I go to the dxm2 all the documentation for it shows that the dehumidifier line goes into the H terminal on the dxm2. However, the cabinet temperature already occupies this terminal on my p2.

    Anyone have any experience hooking up the dehumidifier to a noncommunicating theremostat?

    Any help appreciated.
  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Yes. It's super simple if you have enough wire.

    Just do as ecobee says and then set to DH is heating only.

    BLAKE STARR New Member

    Thank you for the response. I have 8 wires ran at the moment. Is it only possible to have the tranquility to dehumidify when heating? I have a problem with humidity in the summer, so it wouldn't help if it was on only when heating
  4. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Ooops. Sorry was thinking humidifier even though I read dehumidifier. Yeh, your unit will naturally dh in the summer but you can run the dh as well for sure.
  5. Advent

    Advent New Member

    I have exactly this same question!

    I’ve been staring at the wiring diagrams for a while and it looks like the ACC1 relay can also control the dehumidifier function. If I set the dip switches to off-on-off for ACC1 it should think the relay is powering a dehumidistat, in which case the COM1 and N/O connections should assume they’re connected to a dehumidistat. I THINK.

    Could anyone confirm/deny that? I’m not sure how I’d even test that theory short of wiring it up and seeing if something lights on fire.
  6. geoxne

    geoxne Active Member Forum Leader

    It is not clear whether you are trying to DeHum with the geo unit itself -OR- if you are trying to control a whole house dehumidifier ducted to your system and controlled by your thermostat.

    With the geo unit itself, when the DXM2 receives 24vac at the DH terminal the fan will run at a lower speed than normal (adjustable with service tool) to increase latent capacity while running (the ability to remove moisture). To be clear this will only help while the unit is running in cooling. If your tstat can provide a 24vac Dehum signal wire it to the DH terminal on the DXM2 board and the fan speed will decrease to set level.

    If you are adding a whole house dehumidifier, you will have to configure and control wire it to the ACC1 terminals. Configuration and wiring is dependent on the specific equipment to be installed. When the DH terminal on the DXM2 is energized the ACC1 relay will be activated.

    Quick Tip-If humidity is an issue ONLY RUN run your fan in AUTO. If the fan runs with the AC not running the airflow will reabsorb all the moisture on the aircoil and drain pan and reintroduce it to the house. I have seen the RH drop 10% compared to running continuous fan.
  7. Advent

    Advent New Member

    Dehumidify with the geo unit, controlled by the thermostat. The problem is that, with an internal variable flow pump, the DH terminal is already occupied:
    The AOM says that the ACC1 can be used with a dehumidistat, but I'm unclear as to whether that's a relay to control another unit or that would allow connection of a dehumidistat to the geo unit.

    Also, I noticed this in the manual:
    Does that mean that the geo unit would treat a Cooling Stage 1 call as a DH call?

    I really do appreciate the response! Thank you!

    Also, I do have a ClimateMaster communicating thermostat but, aside from diagnostics, I really don't like it. In one day the house is already way more comfortable with the Ecobee than I could ever get it with the CM thermostat. I can still connect it to set up the DXM2 as needed, though.

    Edit: Lastly, I'm in Southeast Alaska. I need the dehumidifier but not AC. It rains 300 days a year here.
    Last edited: Jul 22, 2019
  8. geoxne

    geoxne Active Member Forum Leader

    Your geo unit can NOT dehumidify on demand. Almost all residential units can not. They can only help dehumidify while AC cooling. With the DXM2 H terminal unavailable you can't even control the DH fan speed with your thermostat DH signal to aid in dehumidification while cooling.

    No. DH call does NOT turn on cooling on your unit. A DH call if it was available will reduce airflow to set DH fan speed while cooling and activate Accessory Relay 1 (with Dips set) to control a whole house dehumidifier. With DH control off the table for you, the only thing you can do is set Dip 1.5 to dehumidification which will lower the fan speed to DH fan speed setting only while AC cooling.

    If you have little or no demand for AC and have a problem with humidity, first try to identify and remove sources of moisture in the house. If you care to experiment rent some portable dehumidifiers to see if they help your situation before investing in a whole house dehumidification system.
  9. Advent

    Advent New Member

    The problem with humidity is not sources *inside* the house, it's sources *outside*. Having near-constant rain means the air is very humid all the time. For example, even covered and with plenty of ventilation, I cannot get firewood to season. It molds. Any time someone comes to town I get questions about why everyone has weird-looking bags hanging from their car windows - those are Damp-Rid bags, because otherwise your car interior gets covered in mildew and the car is ruined. I actually do have a small dehumidifier I use in the garage to keep the moisture in/out of the car down; I can move it into the house occasionally if needed.

    Anyways, thank you for your insight about how the heat pump works. I'm glad I didn't try just wiring random stuff up! The lack of a dedicated dehumidification feature explains why the Climatemaster thermostat never brought down the humidity levels. The Ecobee is running AC for DH right now so I'll just set DIP 1.5 for DH mode.

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