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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8326
Experience:  Furnace, A/C and heat pump specialist.
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I have a Trane programmable thermostat on a heat pump system.

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I have a Trane programmable thermostat on a heat pump system. I want to put a Nest thermostat on it. The only wires I see connected are D (green) R (white) and B (black). The lady at Nest said she did not think their unit would be compatible. Is that true? Is the high-end internet controlled Trane thermostat worth the hefty price tag? Are there other units you would recommend?
Hello. My name is XXXXX XXXXX I'll do my best to help. Troubleshooting often requires meters and test equipment. Let's get started and see what we can do.
Sounds like what you have is what is known as a communicating thermostat since there are only 3 wires connected. That is one of the most efficient thermostats you can use with your system.
If you try to convert over to the Nest you will lose the comfort control communications.
Customer: replied 3 years ago.

What would that mean on a day-to-day basis?

I am looking to upgrade to something that will give me internet control through a smartphone. Is there a Trane unit that will give me that?

OK, what the communicating thermostat means is that the thermostat, air handler and outdoor unit are constantly communicating with each other. Most standard thermostats use several wires ,each controlling fan,heat ,ac mode, heat mode,auxiliary heat mode, etc.Basically each one can be pictured as a light switch.For example turning thermostat to FAN On signals the blower to come on just as a light switch would turn a light on. That means each function simply turns something on or off.

With a communicating thermostat, using only 2 to 3 wires, each component of the system is in constant communication with every other part. For example, the outdoor unit knows ahead of time that the indoor room temp is being satisfied, so compressor can drop down to 1st stage.Thermostat has an outdoor sensor, so it can tell air handler to speed fan up or slow it down depending on what the outdoor unit is doing.Amazing what technology has gotten to today, but these things actually communicate with each other through those three wires.

If you want to get something primarily for the remote access, I would check into something like Trane's Comfortlink Smart Control. However, you may have to purchase through a Trane Dealer as they don't like selling to homeowner or even a licensed contractor unless they are a Trane Dealer.

Here is a link to give you an idea.

Customer: replied 3 years ago.

Thanks. This is very clear and it explains a lot. I really appreciate it.


Hope I have been some help with this Rick. Thanks for allowing me to work with you


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