Totaline thermostat to work with two wires

evlap

Hi All,

I'm trying to wire a new Totaline P474-0100 thermostat and facing issues. My old Honewell worked only of two wires R and W and these are connected to a transformer on the furnace (picture). Red and White wires are the ones that go to thermostat. The center wire from the picture is dead.

The new thermostat is coming up, but when it starts calling for heat, its screen goes off and the furnace starts making funny noise.

As far as I understand, there is not enough power for both thermostat and furnace.

There is a suggestion in thermostat's manual to connect a resistor (270 ohm 10 watt) between W and C terminals on the furnance, but it seems like I don't have C terminal there.

From where I can get C wire to power the thermostat?

Any help will be appreciated,
Eugene

Attached Images

 

kennzz05

C is the center terminal with the black wire on it and it needs to be run to your tstat if you look closely at those wires in the picture you should see designations stamped on the red cardboard

evlap

Thanks, I thought the center terminal is dead. I tried measuring the voltage between it and the terminal with the white wire and didn't get anything. Also nothing between the center terminal and the terminal with the red wire. Is this the right way to check?

Also, my current designations are as follows:
C(red wire) Y
C(center, not connected)
R(white wire) W

kennzz05

im alittle confused what are you running with this tstat just turning on the fan?? red or r should be the red wire meaning power to the furnace ( of course it dosent have to be red but thats the standard color for power, white is heat) w should be Wfor heat or G or in your case Y to bring on the fan ( i guess )

maybe this makes it easier
R=24V
G=FAN
Y=A/C
W=HEAT
C=COMMON
which ever terminals you get 24v on in that pic are going to be hot(R)
and common(C)

evlap

I guess, the colors are all mixed up in my case. The tstat runs my steam furnace. I'm getting 24V only on the two left terminals on the cardboard. These were connected to the R and W of my older tstat.

My problem now is that when I connect the two left terminals on the cardboard to R and W on my new tstat, it just shuts off when it calls for heat. That's why I started asking about C.

Am I supposed to have 24V on the center terminal as well?

kennzz05

where do the two black wires go if you hook a 24 volt wire to the common that is a dead short and will blow the tstat and transformer i suspect you are getting feedback and that is giving you your 24v reading the gas valve needs a common and a power to operate your tstat has red(power)in
(white)power out to gas valve
at the valve you can find your common by traceing it back to where it comes from

evlap

Just spent 1+ hour in the basement ... Took both tstats there and hooked them directly to the transformer. My mistake was that I thought R and C on the transformer is what was going to the tstat upstairs. But it was R and W that were going there. So I hooked R and C from the transformer to my new tstat, located W (based on what goes upstairs) and it started working! Will finish it tomorrow and let you know.

Also, the center terminal is actually G (fan, not used) and not C as I thought.

Thanks.

pbservano

You need at least three wires to your wall for your thermostat to work. C-(Blue) connected to the common terminal of your thermostat. R- (red)connected to R terminal. W- (white) this is for your heat.

evlap

kennzz05, pbservano


Thanks. It works now!