All: Here's what's been happening thus far.
The techs replaced the supply ducts with larger supply ducts, replaced the return ducts with larger return ducts, added a return duct going to the second floor, added a by-pass damper, replaced the inducer motor and pressure switch.
The blower (fan) still continues to run after the heat cycle ends, and doesn't stop running until the next heating cycle when the furnace does its start-up routine. This doesn't happen all the time.
In the beginning the problem was related to the limit switch stuck in the open position. Then it became the pressure switch stuck in the open position. I checked the fault indicator light on the control board last night, and it showed that the limit switch was stuck in the open position. I manually cycled it by rapidly switching the power switch off and then on. As of 5am this morning it was working fine.
I notified the tech people who did the work (rightly or wrongly) that I believed that they did what they felt was necessary in order to address the problem, but that the problem still persists. I believe that the furnace at this point probably needs to be replaced, given that the techs have essentially been rebuilding my hvac unit. I don't believe that it's their problem...I believe that I just got stuck with a lemon, and it's time to cut my losses by either replacing the furnace or by ignoring the continuously running fan as long as everything else seems to be operating normally. Note that the hvac unit was installed when the house was built in 2000.
This unit is a high efficiency unit, 90+ AFUE. It's been a problem since day 1. You guys/gals on this message board have attributed part, if not all, of the problem to the fact that I have one furnace, one central a/c unit, and two zones using a motorized damper system. Perhaps you're right.
If the fan continues to run, and everything else appears to be functioning normally, is there really a problem? I've read that a continuously running fan actually contributes to a more uniform temperature throughout the house. The continuously running fan cycles off when the next heat cycle begins. The only nuisance is that at the end of the heating season, when we get those balmy days with cold mornings and warm afternoons, the fan may not shut off, and I'll have to shut is off manually.
Just thought you'd like to know...and if you didn't want to know, I apologize.