I have twinned heating units as w1 and w2. The first unit to come on needs to be replaced; but, until then I need to know how to get the system to heat better. The problem is the fan comes on on unit one (even though the heat does not come on on this unit) when the system comes on and unit 2 is heating. Seems like it is diluting the heat by pulling air through a cold system. Would you recommend turning off the fan on unit one? And if so what is the best way on an older Bryant unit? Would it be at the Thermostat?
Such a setup usually involves a spring-loaded or motor controlled damper specifically to prevent air flowing through a shut-down unit. If you have such a damper then shutting down one unit is perfectly fine.
If they are intended to run together, not alternately, turning one off may cause hot air from the other to flow backward through the other, so you'll get less heat into the house.
Unless (unlikely with an older unit) they are drawing in outside air, the heat put into the house is the same, since the "cold air" moving though one furnace is the inside house air. Since the burner is not working on one unit, you have half the heating capacity you should have. That won't change even if the first unit can be turned off in a manner that does not cause air from the other to backflow through the first.