Fan settings issue

[pldwelle]

On the control panel, when I have the setting to Heat Only, and set to Prefer Gas, if I set the fan to high, it runs the furnace and fan, but if I set the fan to low, the main cabin roof AC/Heat pump fan comes on. Why would the heat pump fan come with these settings? The furnace fan does not seem to have a low and high fan speed, just runs on high speed only as far as I can tell, which is annoying when all you need is a little air movement. I included a picture of my control panel for reference. It shows it is on Auto fan setting so just for reference. I circled the settings where this happens. It does this when I use the Compass app too.

[ncitro]

On the control panel, when I have the setting to Heat Only, and set to Prefer Gas, if I set the fan to high, it runs the furnace and fan, but if I set the fan to low, the main cabin roof AC/Heat pump fan comes on. Why would the heat pump fan come with these settings? The furnace fan does not seem to have a low and high fan speed, just runs on high speed only as far as I can tell, which is annoying when all you need is a little air movement. I included a picture of my control panel for reference. It shows it is on Auto fan setting so just for reference. I circled the settings where this happens. It does this when I use the Compass app too.

I do not have One Control, but I believe the thermostat logic is the same. When running the furnace (gas option) you want the fan set to auto, then it will use the fan built into the furnace only. If the fan is set to high or low when you run the gas heat then it will run the AC unit fan as well as the furnace fan. When using the heat pump and air conditioner you should be able to set the fan to auto, high, or low as you desire.

[pldwelle]

I do not have One Control, but I believe the thermostat logic is the same. When running the furnace (gas option) you want the fan set to auto, then it will use the fan built into the furnace only. If the fan is set to high or low when you run the gas heat then it will run the AC unit fan as well as the furnace fan. When using the heat pump and air conditioner you should be able to set the fan to auto, high, or low as you desire.

Nothing about that mode of operation makes any logical sense to me. I am guessing then that the furnace fan only has one speed, high, correct? Why the AC/Heat pump fan would come on on low setting doesn't make any sense if it is not supplying the heat. Essentially when on low, both the furnace fan and the overhead fan are blowing. Makes for such a peaceful environment!

[howson]

pldwelle

CAUTION: The info provided below is from an old document source -- it may not be accurate.

With that caveat out of the way, the info below should be representative of how your Momentum's Unity X4 board is wired (and thus should interface with the HVAC system).

First, the Unity X4: it's the "brains" behind the OneControl (aka "CompassConnect") system in the rig. Typically in a Momentum the board is tucked under the stairs (camp side) behind the false wall in the storage compartment. What will be referenced here is the HVAC connections on the board.



In the breakout below, note there's a "Z1", "Z2" and "Z3". These are to support up to three air conditioners and a furnace. The "Thermistors" are where the thermostats plug into the board.




Note how Z1 is the only connection that powers the furnace (connection 10). So that's the circuit we're discussing in this thread.

I believe all of the HVAC connections to/from the X4 are discrete (go directly to the thermostat). The OneControl touch panel (and input from the app) execute control of the systems via logic that simulates some of the discrete connections.

What's my point in providing this information? According to what I see in the wiring (again, assuming the information is accurate) the Unity X4 board should support the operation desired (low fan with furnace).

• That conclusion assumes the inputs/outputs to the board from the thermostat are passing the appropriate states, the internal logic of the board is configured correctly, and the system's plenum supports the desired mode.
  • The "plenum" has a relay sub-component that passes signals and 120vAC to the major sub-components in the system. The "plenum" assembly is what you see in the ceiling of the trailer that holds the air conditioner filter.

So what's the takeaway? If the system components are supposed to support the mode, it looks to me like the system could be wired wrong, the logic in the X4 board could be configured incorrectly, or the plenum may not support the desired mode.

This is all being written and thought-through behind a keyboard, so I could be missing something. Troubleshooting this setup to find out where the fault is will take a technician that intimately understands the system and how to properly use test equipment.

Regardless, I hope in some regard this is helpful. If nothing else to inform you, the owner, to allow for an intelligent interaction with your dealer and/or Grand Design Customer Service.

Please follow up if you find out what's going on (even if not "fixed").

Howard

P.S. Anyone else reading this have a late model Momentum like the OP's? Will the furnace fire up with the a/c fan on Low? High? If known, document the actual components (make/model) of the air conditioner, thermostat, and furnace.