Nest Thermostat 3rd Gen Compatibility (Updated w/ More Info)

[Ralpheweotto]

Hi there,

I'm trying to figure out if my system is compatible with a 3rd generation Nest Thermostat. I'm switching from an AprilAire thermostat that was installed with the HVAC system this year.

There are two zones in the house (first and second floor). The second floor thermostat was compatible with no issues and has been working great. I ran into compatibility issues on the first floor.

The install is getting stuck on the T1 and T2 wires. I suspect this is because the first floor has gas heat as well as a heat pump, but unsure. The air handler for the first floor is in the crawl space and has a condensate pump. The outside units are Trane with a condenser (4TTR4024N1000) and heat pump (4TWR4030N1000).

I would welcome any advice on whether this is compatible or not! Thanks in advance!

Ralph

[GBD]

@Ralpheweotto , according to the installation guide for your AprilAire S86nmu thermostat (https://rp.widen.net/content/dcacsoijge/pdf/aprilaire-s86nmu-s86nmupr-thermostat-installation-guide-...), your T1 and T2 connections would be for an optional remote temperature sensor.

As far as I know, none of the Nest thermostats have the option of using a wired remote temperature sensors but rather they use a wireless remote sensor (https://store.google.com/product/nest_temperature_sensor_2nd_gen)

Did you try to install the Nest thermostat without hooking up the T1/T2 wires?

[Ralpheweotto]

Nope I haven’t yet! I assumed it was related to another system. Any idea if leaving off the T1, T2 can damage any equipment?

[GBD]

Just make sure the ends of the T1 and T2 wires are covered with some electrical tape so they don't short anything out and you'll be fine. Worst that could happen is that the nest might not work but you won't damage anything.

You might want to find out where that remote sensor is and figure out if you'll need to add one of the nest thermostat wireless sensors. The sensor was probably added to your current setup because the thermostat is not mounted in a the most optimal position but the people who installed it might have a better idea of why is there than I can provide you.

[Ralpheweotto]

Thanks! I connected the Nest and taped up the T1 and T2 wires. Unfortunately, I'm not getting any warm air coming through. Everything's blowing, but it never heats up. Any suggestions?

Edit: I've set the heat to 68 as a test. Current inside temp is 63. In the last 30 min or so the internal temperature hasn't changed. Outside temp is 47.

[GBD]

That's unfortunate but I don't really have any more suggestions. CoolingWizard (@Jrizzo003)  here on the fourm has much more HVAC experience though so hopefully he can jump in with some recommendations. Other than that, it could be that your best bet will be to get the installer of the original system in to get the Nest working with your system.