Hello All,
Perhaps someone here can answer a perplexing question that I have. I wanted to install a new wifi connected thermostat yesterday, and before I started the job I reviewed the instructions. Then I looked at the wiring that I have going to the thermostat. IT appears that one wire in my system doesn’t comply with anything that I have read online or anywhere else for that matter. This has halted me in my tracks until I can figure it out.

My furnace has W, Y, R, C, and G. However, nothing is connected to the W or Y terminals. As expected, the G goes to G (the fan) on my current thermostat and the R to Rc which is jumpered to Rh (24v out) as expected. It starts getting a bit strange at this point but still understandable. The C (the common or return on the furnace terminal) goes to my air conditioner, then up to the thermostat where it is connected to Y. This makes sense to me as well.

The part that I can’t make sense of is the W connection at my thermostat. One would think that this should follow the same sort of pattern that the Y (air conditioning) followed by going to the heat and then to the common terminal (C). However, instead, following the wire from the thermostat, it runs down to the furnace, straight inside the furnace to the pilot light, then from a second terminal on the pilot light to a terminal on a small cube inside the furnace, then from a second terminal on the small cube back out where it connects to the R on the circuit board. I can’t even fathom how that turns on heat as opposed to tripping some circuit because in my mind it would seem that when the heat comes on the thermostat would be closing the connection from Rh in the thermostat (24v+) to the 24v+ on the R connection at the furnace circuit board. Yet this is how my current thermostat is hooked up and it has worked for years. Where my problem lies, is that because of this wiring, I have no idea how to hook up the new thermostat.

I could add pictures, but with no writing on the square cube in the furnace, all that I would be adding to this little rant of mine is a cute little picture of a black square the size of a golf ball. And the pilot light looks like any other on a 30 year old mid efficiency furnace so there is nothing out of the ordinary there either.

Thanks for any help anyone can provide.

 

W is for heat. R & W for heat
G-fan
Y- condenser if you have air conditioning
R- power
What brand furnace. Why don't you post a picture of the thermostat terminals at the furnace

 

Thanks Mbk3. Thanks for the reply. I understand what the terminals are for. What I can't figure out is why the original owner wired the heat up the way that they did (or even the air for that matter although at least the air makes sense). I can't post a picture at the moment. If it will help I can later. But as stated above, even though there is a W and Y terminal at the furnace, neither was used. Only the C, R, and G terminals are connected. The wire connected to the W terminal from the thermostat goes directly to the pilot light, from the pilot light to a small square unmarked box inside the furnace, then from that box to the R terminal on the outside of the furnace. There are two wires connected to the R terminal at the furnace. One goes directly to the Rc terminal on the thermostat, and the other goes inside the furnace to the little black box. If it helps, I can add pictures later. However, the connections are as stated above.

 

I forgot that I have at least some pics from the inside of the furnace where the W wire connects to.




So the wire comes from the thermostat W terminal and goes to the bottom pic, then to the middle pic, then from that to the R terminal on the furnace. Really, adding the pic of the terminal box of the furnace will just show you four wires. Two connected to the R terminal, one to the G, and one to the C with nothing connected to the W and Y.

 

I can understand why Y is not landed on the furnace. But W not landed is a little confusing. A pilot light does not use a wire, so you must be talking about something else.

 

Pilot light igniter? Not sure what it is called but whatever the bottom picture is....that is what the wire from the W terminal on the thermostat goes to.

 

This is testing the extent of my artistic capabilities. The only thing not seen in this picture, is the terminal box that is attached to the outside of the furnace which would be right to the left of the picture. This shot was taken looking into the furnace from the front with the cover pulled off.

 

OK... that's the gas valve. Some one has bypassed the safeties on the the furnace, not good. In your top pic there is a gray box with a white reset button. That is your high limit and fan switch. That should be in the circuit from the W wire.

 

Not sure if the black box is your tansformer or a relay. Maybe some one else will recognize it.

 

OK. I got my son to take a pic of the terminal box on the outside of the furnace in case it helps for whatever reason. No point in taking a pic of the thermostat because the terminals are the same on all simple thermostats. It looks like a lot of wires because one wire goes to the AC and back and the other inside the furnace and back. You can easily make out the W and Y terminals and see that there are no wires connected to them. The C terminal is on the top (that wire goes to the AC then up to the Thermostat Y terminal), the middle terminal is the Green wire that goes directly up the to thermostat G terminal to control the blower (fan motor), and the bottom terminal with two red wires coming off of it is the R terminal. One red wire goes up and directly to the thermostat Rc terminal. The Rc terminal on the thermostat is jumpered to the Rh terminal on the thermostat with a one inch wire. The second red wire on the R terminal at the furnace goes from there, to the inside of the furnace as shown in the above photo, then back out and up to the W terminal on the thermostat. I know this is repetitive but I thought it would save readers from having to go up and refer to the first post.

 

One more thing. That little black box inside the furnace would be directly on the inside wall opposite the terminal box in the picture below. So maybe that is an inside W terminal? But why would it go up to W on the thermostat and then back down to the R? I can't make head's or tails of this and yet it works.

 

Hey skaggsje....I didn't see your one post until just now about bypassing the safeties. What exactly does that mean. What safeties would be bypassed? And curious that you mention the grey box with the white button. Out of curiosity I press that yesterday and it did absolutely nothing. Is that to control the speed of the blower motor or something?

 

The W wire from stat should be connected to the W terminal on the furnace. What's the model number on the furnace?

 

I'll have to check tonight. I can't make it out in the photo and I'm not at home.

 

If everything is running OK then we are missing something in the wiring.

 

The honeywell grey box has 2 dials in it . One starts the fan in heating mode. The other is the high limit to close gas valve if temp gets to high.

 

The things that I am getting my son to do via telephone

The furnace is a CARRIER WeatherMaker Model # CHB105-TS

 

Ok, let me see what I can find.

 

Can't find anything with that model #. Carrier's usually start with 2 numbers. Yeah, kids come in handy once in a while....

 

OK. I'm home in an hour and a half. I will look myself. I really appreciate your taking the time to check this for me. Like every other project in a 30 year old home that I purchased 10 years ago, one small project seems to be turning into something far more time consuming. I need to correct whatever Red Green duct tape job the previous owner has done. I'm surprised my home inspection didn't catch this 10 years ago. Or the furnace repairman who replaced the motor, or the gas guy who connected my hot water heater.....

 

It's so great being a home owner......

 

The model number is CHB105-TS

 

The furnace is from 1986ish .... so maybe that's why it doesn't show up anywhere on Google. I think the internet was basically education and military in 1986

 

Maybe this will help. I did the best I could with the pic off the inside of the furnace.

 

This is a pic of the total layout.

 

I came in late and this is a long thread. Your wiring looks ok. The safeties in your furnace are on the 120v side of the 24vac transformer. We just had an identical furnace to yours in a thread several weeks ago.

The W and Y screw terminals on the fan center are not connected to anything inside.

 

Thanks PJMax. Can you explain to me the wiring for the heat side? With the W terminal at the thermostat ending up back at the R terminal at the furnace instead of the C which I am fairly sure is the common terminal wouldn't appear to complete any sort of circuit. It would seem like the circuit goes from 24+ down to the gas valve, to that small black box, then back out to the R 24+ terminal on the furnace again.

Also, the small white knob on the Honeywell Grey box inside the furnace (pull Auto, push manual) didn't seem to do anything. Possibly because I pushed/pulled it while the furnace was still running.

I'm actually more baffled by the W wiring and can't grasp why it seems to go from + to +.

 

Did the system work correctly before you decided to replace Stat?if so label the wires as to which wire is on the old stat terminals, and connect them appropriately to the new, main thing is that you have 24 VAC between RH/RC and C.
Geo

 

The system works fine with the old stat, and I am sure it would work if connected to the new one. And I completely accept the info provided to me by the experts here. I simply wanted to understand the circuit for heat because it doesn't make sense to me at the moment. I am the type of person that wants to learn as I go. I can follow advice and hook something up, but if I understand why something is working (or not) then it is a learning process at the same time.

 

Is there a model # on that control with the black what looks to be a relay,can you get a clearer pic of the wiring Dia.on that plate?
Geo

 

I looked at the schematic you posted. A part is below. It shows the 24v transformer, gas valve and thermostat as a loop. Short the stat wires and the gas valve opens.

You need to supply 24v to the valve circuit and it should be from the factory transformer since the safety's are in the 120v line to the transformer.

 

Thanks everyone. Appreciate all the input. I found this forum while looking for answers. I'll try to 'give back' when I can. My expertise is in computer repairs (hardware and software). 20+ years.

 

Oh, and Geochurchi, here is a closer shot of that black box.



The red wire goes to the gas valve. The yellow goes out of the furnace and to the R terminal on the control board directly opposite this black box on the outside of the furnace.