Installing Nest to replace Carrier thermostat

Old 10-03-19, 12:02 PM
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Installing Nest to replace Carrier thermostat

Hi All,
Need some help, wife brought home a NEST thermostat so I was doing research to see if I can do this myself but keep running into more questions than answers.

The central air unit in comfort series and I attached the heat unit specs. If more info is needed I can attach more pictures.

I took off the Carrier thermostat and there are only two wires(v+ and Vg which are red and black respectively). Which the NEST website said was not compatible, but I read that I could bypass the control module and route it to the NEST. So then I found the control module and opened it to see two sets of red(Rc), white(W/W1), yellow(Y/Y2), black(C), and orange(O/W2/B) wires. Was only expecting one set based on other posts, not sure what to do next since the NEST appears to be only expecting one wire each. Any help would be greatly appreciated!

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Last edited by PJmax; 10-03-19 at 10:21 PM. Reason: reoriented/resized pictures
Old 10-03-19, 10:39 PM
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Welcome to the forums.

You have a communicating system there. The thermostat is probably a higher end model with many functions and talks to the control module on two data wires. You have a heat pump system there and a set back thermostat is not the most advantageous to it's operation. Rather then setting the temps back.... the heat pump should just be allowed to run.

That aside..... if you want to carry on you will need to verify that you have enough wires to the thermostat location. You should. Carefully pull out the red and black wires and confirm there is an 8 conductor cable there. Turn off the air handler before doing any wiring work. At the control end..... the D1 and D2 (red and black) wires should be that same cable with the extra wires just folded up. ID the thermostat cable at the control end. It's one of the three coming into the module.

Take the 2 red wires out and add the D1 red t'stat wire. Wire nut the splice.
Take the 2 black wires out and add the D2 black t'stat wire. Wire nut the splice.
Take the 2 white wires out and add the white from the t'stat cable. Wire nut the splice.
Take the 1 green wire out and connect to the green wire from the t'stat cable. Wire nut the splice.
Take the 2 yellow wires out and connect to the yellow wire from the t'stat cable. Wire nut the splice.
Take the 2 orange wires out and connect to the orange wire from the t'stat cable. Wire nut the splice.

At the nest.....
Red - Rh
Black - C
White - W2/AUX
Green - G
Yellow - Y1
Orange - O/B

The nest will need to be programmed for heat pump with back up electric heat.
Old 10-04-19, 08:33 AM
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Just so your aware, of the problems that Nest has and causes, before you go through the trouble of installing one.
I’ve lost count of the number of them I’ve removed due to various problems. I’ve removed 2 Honeywell thermostats due to problems over the course of 18 years.
Your Carrier thermostat is likely superior.
Your heat pump will run best when left to a consistent setpoint. If you would like to adjust the setpoint in heating mode, a thermostat with auxiliary heat lockout is best.

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