Ethernet Wired Thermostat - Nest / Installing proper wiring

mike212

This is a case where I know a little and need help filling in the important details. For my AC, (high velocity Unico Airhandler), the thermostat is wired using Ethernet cable (8 thin wires). This thermostat is just for AC, no heat. It works fine with a standard thermostat but my wife is really pushing me to upgrade this to a Nest.

I tried a Nest and it worked sometimes with this wiring but would occasionally stop working for a period of time. After troubleshooting with Nest they said its because I'm using telephone wire instead of proper thermostat wire.



I found the wire and how its run and traced it back from the thermostat to my Unico airhandler. I have run 18/5 wire alongside the currently used ethernet cable but I'm not
sure how to connect the new 18/5 wire to my Unico air handler.


The gray ethernet wire enters that box on top of the air handler along with two other 18/5 wires. One of those 18/5 wires goes to my condenser outside. The other I'm not sure where it goes.

I assume I need to open this box and then connect my new 18/5 wire wherever the gray ethernet wire is currently connected. I shut off the AC power at the circuit breaker however I'm concerned its not really off since a non contact voltage tester pen shows a high level of power on that yellow electrical wire entering that box on the right.

Am I on the right track here to open that box and connect the 18/5 wire to the current ethernet wire connection spots? Here is my current thermostat wiring...

Zman

The new wire should work just fine. You are going to need to figure out how to wire it to the Unico unit itself. Do you have a wiring diagram for that unit? Sometimes it is on the back of the access door or in the provided manual. Just a picture of how it is wired now might be enough. If you decide to open the unit, be sure to turn off the power so you don't make your hair curly or let the smoke out of the parts inside.