Tony Hwang wrote:
Nate Nagel wrote:
Don Wiss wrote:

On Mon, 18 Feb 2008 19:03:00 -0600, CJT
wrote:
mr. spam wrote:



I want to replace the fan motor with a 2 speed one

i want to add a switch to the furnace so i can have the fan on all
the time in slow speed. then when the burner or the ac comes on
it will change to high speed.



I think many (most? all?) furnace/AC combinations already
incorporate dual speed fans. Are you sure it doesn't already have
the capability you seek? You might just need an appropriate
thermostat.



I believe you are correct. The heat uses the low speed and the AC
the high
one.

Don www.donwiss.com (e-mail link at home page bottom).


Actually mine has several speeds, not sure how many. only three can
be controlled from the thermostat however. By moving wires around
on the circuit board you can change which speeds are used for which
events. I think the way it is set up now, if you command the fan
"on" from the thermostat, it runs at a low speed, in "heat" mode it
runs at a medium-high speed, and on A/C it runs at the highest speed.

I have on occasion found it useful to command the fan on even when
the furnace is not running, e.g. if someone is doing a lot of
cooking in the kitchen on a cold day it can be cold upstairs because
the thermostat is on the first floor, keeping the air circulating
not only cools the kitchen but tends to even out the temperature
throughout the house. I've also completely closed the supply dampers on
the first floor,
but that's primarily because of the dramatic difference in insulating
properties between the first floor (block walls with brick facing)
and the second floor (sticks 'n' shingles) - I do plan to have the
second floor insulated but not until I'm done fixing all the wiring.

Anyway back to the topic at hand... it sounds like the OP does need a
new thermostat, and probably also needs to pull a new cable between
the thermostat and furnace to allow for more functions. (typical
heat only scenario would only require two wires, but heat/cool/fan
only would require at least four.)

nate

Hmmm,
My impression is OP has a OLD furnace which does not have multi-speed
fan and or elaborate electronics control board.

LOL

--
Zyp