Hello,

Our Diamond 80 furnace blows cold air when thermostat is set on 69F. So far I have cleaned flame sensor, replaced control board, limit switch and air pressure switch. The flame is coming on and works fine (no codes either). The first floor still gets somewhat warm air but the warm air does not reach second floor. Does anyone know what the problem is?

Is the blower motor running?

Yes, the blower is working. What else do I need to check?

Check to see if there is some sort of damper int the duct going to the upstairs