On Tue, 10 Dec 2013 16:12:10 -0500, David L. Martel wrote:

Read section IV of the manual.
It explains what should occur and when in the heating process.

Here's my summary of the PDF, after reading it a couple of times:

1. Red wire is 24VAC hot.
2. Thermostat "calls for heat" by connecting Red to White.
3. Thermostat "calls for fan" by connecting Red to Green; but the
fan is actually controlled by the fan PCB so the thermostat only
tells the fan PCB if it's to run continuously or automatically.

Details:
Thermostat "calls for heating" by connecting Red to White.

Power goes from the 24VAC Transformer - Fusible Link - Limit Switch -
Vent safety shut-off switch - pilot ("pick" & "hold" gas valves)
such that pilot gas flows.

Power also flows to the igniter, which ignites the pilot flame.

60 seconds after pilot, safety pilot switches its contacts and energizes
the main valve portion of the gas valve, where, about 10 seconds later,
the main gas valve opens, and the gas is ignited by the pilot flame.

75 seconds after pilot, the fan control board activates the fan on low
speed.

When the thermostat "is satisfied", the connection between R & W is broken.
Gas is immediately stopped to both the pilot and main burners.
The blower continues for about 100 seconds.

If the furnace overheats, the Limit Switch opens.
http://farm3.staticflickr.com/2814/1...0de1c8bd_o.gif
If the furnace overheats in the vestibule, the Fusible Link opens.
http://farm8.staticflickr.com/7323/1...56224304_o.gif
If the furnace overheats in the vents, the Vent Safety Switch opens.
(I have not found this VSSS yet.)
There is also apparently a Lockout Timer for the gas flow:
http://farm8.staticflickr.com/7323/1...56224304_o.gif

The PDF does not explain how that lockout timer works though ...