Stormin Mormon wrote, on Sun, 21 Dec 2014 18:39:15 -0500:

First step is to seek for the air filter, and replace
it.

I opened up all the vents, and removed all the filters.
https://c4.staticflickr.com/8/7576/1...eb92f0c2_b.jpg

Also see if the blower wheel spins while the furnace
is on, and calling for heat.

Is this the "blower wheel"?
https://c4.staticflickr.com/8/7471/1...173421dd_b.jpg

It spins freely manually (but never turns when the blower is
running).

I also replaced the batteries, in the controller, even though
they had tested at 1.4VDC open circuit (the new ones are
1.6 volts open circuit).
https://c4.staticflickr.com/8/7534/1...12b21a95_b.jpg