Nest Thermostat installation

I have bought a Nest Thermostat hoping that I can make my "TemperZone" branded HVAC a smart one. After nemerous amount of failures and 2 weeks of reasearch I am looking for some forum help. The Ozbargain way ;)

I have 4 ports in my current system:
Port B with Yellow wire and Port A with Green. They go to RS-485 Comms.
Port GND has black wire and Port 12v+ has Red wire and they got to Power Supply.

In my Nest, I don't have ports that specifically mentiones the posrts as above but it has the W, R, B, R, G, Y ports.
I have tried re-porting from Temperzone to Nest Thermostat but expect Power, nothing else gets picked up when I setup the thermostat via the Google Home app.

I have been through many forums and reda articles and people's experiences.
Do you have any luck or do you know any electrician who can help with setting this up?

So far I found one Canberra based company who has installation experience but unfortunately they don't provide service in central coast.

Any help guys?


  • Try directly contacting the manufacturer.
    I did (through an installer) with my Braemar unit and they had a wiring diagram for the Nest that I simply could not find online.

  • Something to be aware of is that the Nest Thermostat, if you can get it to work, only sends on and off signals. It uses its own smarts to determine when to do so. But it doesn't send the extra information that enables the inverter in modern systems to save power by running at less than 100% when the sensed temperature is close to the target temperature.

    This means the system will cycle between 100% on and off, the same way older systems (before inverters were built in) worked. Yes it works, but it's less power efficient, and places additional stress on the system by flipping between 100% on and off. The more frequent flipping between on an off is more noticeable/disruptive as well.

    Above is the main reason why they don't sell the Nest Thermostat locally.

  • I could be way off here, but I think that the Nest device is a switching thermostat device. The fact that your HVAC has RS485 terminals would indicate that you would need an RS485 thermostat with wifi control.