A/C and Cool to Dry setting on Learning Thermostat

[joloeryu23]

I have a gas furnace and A/C unit and have started using the A/C as it's getting hot enough here now. My system is a Rheem system and has the ability to dehumidify with the A/C by using a special mode that slows the fan (I do not have a stand-alone dehumidifier).

In the Google Home app there's new settings I haven't seen before with the previous Gen thermostat for cool to dry. Instead of a simple cool to dry setting, there's now a Dehumidifier setting (enable/disable) and a Humidity Helper (HH) setting.

Now, I cannot disable HH, it's grayed out and says it's required to work with my type of system. But the Dehumidifier setting was enabled by default, which to me means it thinks I have a stand-alone dehumidifier? Or is it enabled because my system supports a dehumidification mode?

Also, regardless of what setting I chose, if I look at my air handler/furnace, the display has Cd or cd (2-stage or one stage with dehumidification) even if the humidity is well below the setting in the app of 70%. 

What the heck is going on here? Should I leave the Dehumidifier enabled, or disable it? And why can't I disable HH?

[Derickf]

Hi @joloeryu23,

Thanks for reaching out to the community. I understand you're seeing some new dehumidification settings in your Google Home app for your Nest Learning Thermostat because of your Rheem furnace and A/C's built-in dehumidification mode. I'm happy to assist.

To gather the necessary information, please answer the following questions:

• You mentioned having a Nest Learning Thermostat; could you please confirm its generation? This article might be helpful: How to tell which Nest thermostat you have.
• Does your HVAC system's control board include a dedicated humidifier terminal?

I'll be waiting for your reply.

Best regards,

Derick.

[joloeryu23]

It's the Gen4, sorry I didn't mention that.

I'm not sure, i did have to change some wiring for the dehumidification mode though, which is what "cool-to-try" is as far as I remember. It slows the fan down letting the AC run longer to remove some moisture.

I'm confused as I used to see "cool-to-dry" on my Gen3 when it was working, and cd or Cd (small c indicating stage 1 cooling, large indicating stage 2) would show up on the air handler's LCD display indicating it was cooling with dehumidification.

Now though, it seems like I'll see cd or Cd show up, but neither on thermostat nor app does it indicate cool-to-dry is working (or humidity helper). So, I'd like to know a lot more about what exactly is happening.

It's really important thermostats and apps reassure people that things are working as expected. We need to know exactly what they are doing. This equipment costs thousands and people don't like taking chances with stuff that costs that much.

[joloeryu23]

I also want to mention that the documentation for this is very sparse. It needs to be much better documented with much more in-depth information. 

[Derickf]

Hi there!

Thanks for your reply. I understand you have questions about the Nest Learning Thermostat (4th Gen)'s new dehumidification settings in the Google Home app, since your Rheem HVAC system has a built-in dehumidification mode. I'm happy to share more information about this feature.

The Humidity Helper (HH) is an advanced feature that proactively uses your system's fan-slowing humidifier and is often automatically enabled and required if your system is compatible. The separate humidifier setting simply controls whether your Nest uses this capability. While the "cool-to-dry" label isn't explicit on the Nest Learning Thermostat (4th gen)'s display or app, unlike the Nest Learning Thermostat (gen 3), your air handler's "Cd" or "cd" indicates the system is correctly engaging its dehumidification mode. You can confirm it's working by monitoring humidity levels in the Google Home app and observing slower fan speeds during cooling cycles.

I hope this information helps.

Best regards,

Derick.

[joloeryu23]

Thanks. So selecting "A/C integrated dehimidifer" is appropriate here I guess?

Also, there's a setting for relative humidity (RH) and it's set to 55 by default so I've left it there. However, in the HH section advanced configuration humidify threshold has an addition setting, 70% by default. So which setting is it?

Am I alone here thinking this new configuration in the 4th gen is really confusing?

[joloeryu23]

I had my relay set to active dehumidification mode when "closed". However, my manual states dehumidification mode is active when the relay is open. Thus, I had to change the setting in the app to only activate dehumidification mode when the relay is open. 

Because I had it set to activate when closed, every time it ran the AC, dehumidification mode was activated.

The problem is solved. Just had to read the manual again, lol.