This was the response I received to hooking up my Gen3 Nest Thermostat to a new Carrier Infinity Air Handler and Compressor.
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Hi Rob, I'm Brian with Comfort Solutions. Rich asked me to reach out to Carrier technical support to look into connecting your new air handler with your Nest thermostat. As we suspected, it is not a feasible approach.
Communicating equipment is specifically designed to be controlled by a special thermostat, because in their operation, the thermostat becomes the brains of the system. In a conventional system, the thermostat is nothing more than a temperature activated on/off switch, and the system operations are managed by a control board in the air handler. A communicating system places this function in the thermostat itself, where it makes intelligent decisions about what stage of heating and cooling to run, how fast to turn the fan, and how long to run to achieve the setpoint based on data it is receiving from the air handler, the outdoor unit, the temperature in the house, and even the outside temperature. This allows it to provide maximum comfort and efficiency.
The air handler is compatible with a conventional thermostat in what Carrier calls "Emergency Mode". This means that, in the event that the Infinity control breaks, a conventional thermostat can be used temporarily to provide heating and cooling. This allows a technician to get a system operational in such circumstances as we have a bad control and it might take a day or two to come back with a replacement. However, a lot of functionality is lost: Not only will the system not stage correctly, a conventional thermostat will not properly engage the blower motor. This will cause the coil to freeze if left in such a configuration for more than a few days. Think of it like driving on a spare tire: You can make it to the next gas station, but you're not going to want to leave it that way for the long haul.
I understand the primary reason you want to keep the Nest is that you have temperature averaging sensors throughout the house. Carrier does not have a similar setup for the Infinity system, mainly for one reason: It doesn't need one. The main reason people find they have uneven temperatures is problems with airflow, usually because the ductwork is less than optimal. But the great thing about the Infinity which sets it apart from other units is its ability to overcome sub-optimal ductwork. The air handler has sensors which monitor the speed and pressure of air in the duct, and automatically adjust the blower operation to make sure the optimal quantity of air is being delivered across the system. This can be further enhanced by running the fan in "On" instead of "Auto", which means that even when the system is not calling for heating or cooling, it will run the fan in the air handler, which tends to average out the temperature throughout the house by taking air from all the returns, mixing it, and redistributing it. In 99% of cases, this works A LOT better than temperature averaging sensors, which always result in temperature imbalances through the house.
I hope this information is helpful! I would only add in closing that, in all the years we have been installing Infinity air handlers, no one has EVER called us back later wanting to go back to their Nest thermostat!
----------- Original Message from "Koller, Joe" ---------------
Date: 2024-06-03 12:01:44
Subject: FE4 Air Handler Control
To: brian.downs@comfortsolutionsinc.net<brian.downs@comfortsolutionsinc.net>
Brian,
Below is an excerpt from page 13 of the install manual for the FE4 air handler.
As I mentioned in our conversation, the air handler was designed to be used with the Infinity controller. Using a standard thermostat will reduce functionality and could also not allow the electric heat to come on. Blower motor control could also be erratic.
Emergency Heating and Cooling Modes
Fan Coil Control ca provide emergency heating and cooling using a common heat/cool thermostat in the event that there are no system communications, fault is in User Interface and no replacement is immediately available.
To activate these modes, the thermostat and outdoor unit must be wired as a common heating/cooling system to fan coil control RGWYOC terminals.
Note: These emergency modes do not provide the level of comfort and efficiency expected by the consumer and should only be activated when User Interface cannot be replaced immediately.
All warranty claims must be submitted within 30 days of repair.
Joe Koller | Customer Assurance Manager
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CE | 7841 Coca Cola Dr Suite 200 Hanover MD 21076
Office: 1-866-902-4822 Option 3
