Wireing on Honeywell r6660d thermostat.

[MB9]

Hi all I have honeywell r6660d thermostat which has two neutral  wires joined and two brown wires joined. Also black wire into A and gray wire into B terminal. Can I use third generation nest. If so can help with  wireing  dieogram. Thank

[zoeuvre]

Hi MB9, 

Thanks for posting here in the Community forum and for showing interest in our Nest Thermostats. If your current thermostat wiring configuration has the non-standard labels of A and B which means that your system is proprietary. 

Proprietary systems aren’t compatible with Google Nest Thermostats. However, some proprietary systems can be rewired by a pro installer to be compatible.

Let us know if you have any other questions. We're happy to help. 

Best,

Zoe