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The Daring Dufas[_7_]

On 10/23/2010 7:41 AM, wrote:
On Oct 22, 5:01 pm, wrote:
wrote in message

...

Douger,

If you get one that says it doesn't work with heat pumps or multi-
stage furnaces it should just need the three wires. They are also
usually cheaper. If you have a multi-stage you may be hosed.

I'll probably be doing the same thing for my daughter when she buys a
new house, so let us know how it turns out.

dss

I'm not following you.
Are you saying I only need to connect 3 of the wires?

Typically you have 4 wires:

hot wire, ie current source
heat on
A/C on
fan on/off, ie so you can have the blower run all the time or only
when heat or AC makes it go on.

Your problem is very strange, because per above, nothing from the
thermostat should have an effect on the inducer fan. That is
controlled by the furnace contoller/logic board. The thermostat justs
connects the hot wire to the heat wire to tell the furnace to fire
up. From there, the furnace controller starts the inducer, turns on
the gas, ignites it, starts the blower, etc. When the thermostat
opens, the furnace starts the shutdown sequence.

How long have you let it just sit there with the inducer running after
the furnace shuts off? Does it just keep running indefinitely?

The only thing I can possibly think of is I think some thermostats
steal small amounts of power from the circuit to keep batteries
charged. I don't think most of them do that, but believe some do.
It could be that having that small current flow even when the heat
circuit is essentially open is somehow disrupting the controller in
the furnace. But that seems a long shot.

Might be time to get a HVAC pro.

I sell digital thermostats that can use either/or batteries and 24 volts
AC from the air handler. The standard color code for wires for the
thermostats will give you 24 volt power for the 'stat from the red and
blue wires from the air handler/furnace. I leave the batteries in them
so no presets are lost in case of a power outage. An advantage of 24
volt power is a continuously lighted display can be programed. It's a
good thing to have in a dark hallway at night. The simplest hookup for
a furnace powered digital 'stat uses 5 wires: red, white, yellow, green
and blue.

red - white = heat

red - green = fan only

red - yellow = AC

red + blue = 24 volts ac power

TDD