Bryant plus 90 furnace, only runs heat when fan postiion is set to on and smells like smoke coming out of the vents. The furnace bod heats up to an exterior temp of 120 degrees, the inverter fan runs and the blower fan runs without any noises. You can feel air blow out of the vents closest to the furnace will have a decent blow, but one is below the furnace and the other is in the basement only 4-5 feet from the furnace. All of the other venst do not have hardly any air flow blowing out of them. All connections are good, fuses are good, breaker is not blown and the lower safety switch works that is on the lower panel where the main blower is. I have tried 2 sets of new batteries in the thermostat and it does not change anything. Any ideas on what it could be?