Fan with Whole House Dehumidifier

[JonM2]

I recently installed an Aprilaire whole house dehumidifier. I connected all of the wires from the thermostat that go to the air handler, to the dehumidifier. This enables the Aprilaire to turn off its compressor when the AC in the air handler is on. Works great. This way I am not heating and cooling the air at the same time.  I also added a relay that lets the Nest thermostat command the dehu on and off depending on the humidity reading at the thermostat. That works well too. 

The issue I have is it seems like Nest wants the air handler fan to run any time the dehumidifier is on. I would rather it not do this and instead, when Nest wants the Dehu to run, just use the fan in the Dehu which is smaller and quieter than the air handler. I want the air handler fully off. Is there a setting to do this I am missing?  I don’t think it’s a wiring problem. 

[zoeuvre]

Hi JonM2, 

Thanks for reaching out to us. The behavior you're experiencing with the Nest Thermostat wanting to run the air handler fan whenever the dehumidifier is on is likely a default setting in the thermostat's configuration. Unfortunately, the Nest Thermostat does not have a specific setting to control this behavior directly. But there might be a workaround you can try. You mentioned that you added a relay to allow the Nest Thermostat to command the dehumidifier on and off based on the humidity reading. You could try wiring the relay in such a way that it interrupts the signal between the Nest thermostat and the air handler, effectively preventing the Nest Thermostat from turning on the air handler fan when the dehumidifier is activated.
 
It's important to note that modifying the wiring and using relays involves working with electrical components, so it's recommended to consult with a professional HVAC technician or an electrician to ensure the setup is done safely and correctly. Additionally, keep in mind that modifying the original wiring or configuration may impact the warranty or compatibility of your HVAC system, so it's always a good idea to consult with the manufacturer or a professional before making any changes.

Let us know if that helps.

Best,

Zoe