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Do you have an unused wire in the bundle at thermostat? If not there are a couple of options. Best to is to run a new wire with enough wires for a C.The other option will require you to give up the FAN ON option.
OK now the fan ON option just allows you to turn the fan on without any heat or AC, just blower,Do you think there will be times when you want to turn on just the fan. In AUTO position, fan will cycle with the heat or AC.
Ye very few people actually use the FAN /On feature on their thermostat.As mentioned it just lets you run fan to circulate air without having HEAT or AC on. Do you ever just run your fan?
Excellent.This is the most simple and practical way to solve your problem.All you are sacrificing is that FAN option.
Here is what we will do.
1. Move the wire currently going to G at thermostat over to C
2. In furnace do same thing.Move G wire over to C
3. Now add a small jumper either at thermostat or on furnace board from Y to G
That jumper signals blower on anytime the Y is energized for compressor in outdoor unit to come on,so fan runs on call for Cool.Fan is controlled through furnace controls in heat mode.
Take your time. This will work and will solve your problem.You can rate now and return to the question for up to 30 days at no addidtional charge to follow through or you can do this and then come back to rate question.Expert is not paid for assisting you until you rate answer. Bonus always appreciated if you feel justified when finished.
Thank you. Now if for any reason you ever want to add that FAN ON option back, there is another way to do this.It is a little more involved and requires an adapter that costs about 25 bucks. It is called an "Add a wire" adapter. See links below for how it works and an example of where you can purchase.
But the simplest and most practical is the way explained earlier.