Current Honeywell thermostat has 6 wires. Four are connected from thermostat to Honeywell Wire saver module at furnace = C, W, Rc, K (combined Y and G at the Honeywell Wire saver module), and two connected from thermostat directly toHoneywell Fresh Air Ventilation Damper YTH8321WF1036/U = U1 and U1.
I installed Nest 4th generation.
Setting 1: I connected K (from wire saver module) to Y and both U1 wires to AQ+ and AQ-. Thermostat operated Heat and Cold normally and was able to open the Ventilation Damper but won’t turn fan on without heat or cold on. Help Articles mention a wire in G for fan to turn on outside of Cold/Heat, so went to setting 2 below.
Setting 2: Since thermostat is far away from furnace, running an additional G wire isn't possible. Reading that nest can run without a C wire, decided to use C wire between wire saver module and thermostat as G. I moved it from C to G in thermostat and connected wire directly to G port at honeywell wire saver module going to furnace motherboard. I did not factory reset the thermostat and upon reconnecting the face Nest recognized a G wire and Home app surfaced option to switch on Fan during Ventilation. Once "Activate Fan" option was selected in Ventilation, fan will kick on every time the ventilation damper was opened. It worked great, until we switched to heat mode. In heat mode, thermostat will open up damper, which then kicked on fan before furnace heat started and system gave error - will start, stop, start, stop…fan will blow with no heat, then stop and start again - the motherboard light will go from green to red to green to red.
Question for Pros: In Setting 2 above, can we override Ventilation from turning on Fan in Heat mode so only ventilation damper opens but the fan doesn’t start alongside, instead Furnace starts it when required? Somehow I am unable to post any photos here!
