On Monday, December 7, 2015 at 11:01:35 PM UTC-5, Micky wrote:
On Mon, 7 Dec 2015 04:31:14 -0800 (PST), trader_4
wrote:

On Monday, December 7, 2015 at 3:33:07 AM UTC-5, Micky wrote:
I have an old furnace with a one-speed-at-a-time-based on the wiring
fan motor.

I once rewired it, using the schematic, to see if I could find a lower
speed, so I know the schematic is correct, but in my dotage, I can't
understand it!

It calls it a "direct drive fan motor" and it has 4 wires coming out
of it. It appears that either 2 or 3 wires are to be connected at a
given time, although that doesn't correspond to my vague memory.
The wires a

White Common, connected at all times
Black High, perhaps connected at all times, if you go by the
schematic
Blue Medium
Red Low

The schematic shows 2 wires connected to the motor and a iiuc a 3rd
optional wire.

What's unclear? It has three possible speeds. If there are only
two wires going to it, pick you speed. If there are three wires
going to it, then one of those is for heat and one for cooling.

If that were the case, that would be certainly make it unclear to
someone who didn't expect that, who had never seen a fan motor hard
wired for two different speeds.


It is the case and it is clear to everyone reading this, except you.



But, no. There is no separate heating and cooling speed.


So then it's as simple as can be. Put the one wire on the
speed of your choice.


The schematic is unclear, perhaps incorrect in this one small part,
but I did't post this when I wrote it because I figured out the rest
of the fan relays and enough of my memory came back that I lost
interest in the details of the fan.

Typically cooling is on high, heat would be on medium.