I bought this new house which has Lennox Furnace Model G20.

My problem is this unit always blow. When thermostat reaches the desired point, the heating/cooling stops but fan continues to run.

Did some research and learnt that this unit can support a continuous fan feature in which a switch is added to the system to run a fan at low speeds continuously.

My unit did not have this switch, instead the CF (continuous fan) pin of the controller circuit is directly connected to third speed tab of the fan, while red pin is attached to the fourth one.

I did disconnect the CF cable to try but fan stopped working while the system ignites and fires up. I stopped immediately.

Is there a way to use the system with activating the fan when the heating or cooling is on?

Thanks in advance