On Monday, December 22, 2014 11:24:39 AM UTC-5, Stormin Mormon wrote:
On 12/22/2014 11:12 AM, Danny D. wrote:
My Fluke 75 is a good meter, which I've had for something
like 30 years. So, *using* a meter isn't at all a problem.

The problem is knowing what measurements to take.

To that end, this control board summary is a start:
https://c4.staticflickr.com/8/7511/1...a7b9a83c_h.jpg

As is this wiring control schematic:
https://c1.staticflickr.com/9/8616/1...d2721b93_h.jpg

And, of course, as is the overall furnace circuit schematic:
https://c4.staticflickr.com/8/7560/1...e91c4626_b.jpg

All of which I'm new to, but, which I will print and pore over
to see what basic control and power inputs to test with my
trusty DMM.


Black is hot, white is neutral, and green is
ground. You test at the little box I mentioned
earlier.

If it's the 31 code, I suspect you've got a bad
limit switch, not enough air flow, and the limit
switch finally gave out. I've seen two of those,
this year so far.


It's nothing to do with airflow. He says he gets the flashing
from the LEDs indicating a fault as soon as power is applied,
before there is even a call for heat.