Nest Learning tstat gen3 & Bryant variable speed system

[WilliamB]

Usual question / issue. I have a nest gen3 learning T-stat (3 in total). Was working great with 30 y/o gas fired furnace and electric AC using 5-wires on t-stat (5th for humidifier ). 

new system installed is a Bryant / carrier 4ton variable speed system. Not sure if I need to upgrade wiring to 8-wire. System is running but only appears to have one fan speed. If I’m researching correctly, this is not fixable. 

TIA for any help. 

[BernardRG]

Same question.  Installed a Bryan 38MBRCQ48AA3 Heatpump, with a 40MBABQ48XA3 Air Handler.  I think they are variable speed / stage and have the standard wallmart thermostat.    I have seen Gen 3 is compatible but does it take advantage of the variable speed or multi-stage features of the heatpump/airhandler.    

or does the Air handler manage the speed once the house hits the right temperature to maintain it at lower speed.   Basically want the air con /heat to go on to right temp and maintain as efficient as possible. 

Current thermostate is KSACN1001AAA

Thanks

[Markjosephp]

Hello everyone,

Thanks for reaching out to the Google Nest Community Forum.

Technically, your systems are Nest Learning Thermostat compatible, but the fans will only operate at a single speed. With the variable speed, the fan is constantly modulating faster or slower depending on what temperature the thermostat tells it. It's quite tricky when talking about efficiency, as the system and the thermostat provide energy efficiency. However, it will lose some of the efficiency benefits that a variable-speed furnace provides.

I'd suggest contacting an HVAC technician if rewiring is needed.

Best,
Mark

[Markjosephp]

Hey there,

Checking back in — how's it going? Still need our help?

Thanks,

Mark

[Markjosephp]

Hi folks,

I'm checking in to make sure that you've seen my response. Please let us know if you have any additional questions or concerns before we close this thread in 24 hours. 

Regards,

Mark