Last night I had replaced my working noisy buzzing Honeywell mercury t-stat with a quiet programmable Lux t-stat, reconnected the respective R to R, G to G, W to W and C (blue) to the RH/RC terminals on the t-stat just as the instructions required. Then I attempted to turn on the heat through the t-stat. The furnace fan engaged, but the spark ignitor did not engage and there is no heat.
When I tried to switch the t-stat off, the fan continued to run. The only way I am able to turn off the fan is by disconnecting the wall plug or turning off the furnace fuse box. When I replaced the new t-stat with the original one, the fan still continues to run without heat. There is no smell of gas.
Short of calling in the gas company for a cursory check or else a contractor for an estimate, where did I go wrong or what may be wrong with my 17 year old Day and Night furnace?
(Thank you again NorthernHeat for your response and help!)

[QUOTE=normtoy]Last night I had replaced my working noisy buzzing Honeywell mercury t-stat with a quiet programmable Lux t-stat, reconnected the respective R to R, G to G, W to W and C (blue) to the RH/RC terminals on the t-stat just as the instructions required. [QUOTE]

R-R Good
G-G Good
W-W Good
C(Blue)-RC/RH OOPS!

I don't have the manual for your thermostat here, but the RC/RH terminals on all of the thermostats I've ever installed stood for RC(ooling) and RH(eat) and were used for 2 transformer type systems. There should be a C(common or neutral) terminal on the thermostat. The first three wires are correct, but check the furnace and see if the blue wire is hooked to C on the furnace terminal board. If it is, it must go to C on the stat. If there is no C terminal on the new thermostat, it may be battery powered only and not use power from the furnace.

By hooking R to R and C to RH/RC you've created a short through the stat.

While you're looking at the stat wires in the furnace, check and see if your fuse is blown-you may only need a new fuse (3amp blade type), but you may also need a new thermostat and transformer.

So... you should be wiring like this (if it's to industry standard):

R-R
Y-Y (for A/C)
W-W
G-G
C-C

And if you have RC and RH terminals, simply jump them together and put the R wire there UNLESS you have a transformer in your A/C condenser AND another in the furnace (2 transformer system). If there's no air conditining in this system, connect R to RH and you're done-no jumper needed.

2 things about this post bother me. The first is a noisy, buzzing mercury bulb stat. Was this an old Chronotherm analog programmable? That's the only one I can think of that could fit this description. If it's a T87 round, then I would have this looked at-the only sound they'll ever make is a *crunch* if you step on one. The second thing is the Lux stat having R, RH, AND RC terminals. Usually you have R or RC/RH but not a combination of the two.

Frdbrkl,

You're right. I goofed on the wiring & explanation. The replacement t-stat is a Lux TX9000 and the fuse was not burned out. The LUX instruction wiring diagram for 4 wires & 1 transformer recommends:
Y- Y, C*, 6
G- G, F
W- W, H, 4
RH (RC-RH jumper provided)- RH, RC, R, V, 5

Later tonight, I will re-attempt to install the new t-stat (correctly this time) and hook up the W-W, G-G, R-RH terminal (that is jumped w/RC) and since I do not have an A/C, the yellow has not & will not be included;and I have one question about the blue wire- On the original t-stat, the blue wire was connected to "C" terminal. Since there is no C designation/terminal on the new t-stat, the wiring diagram of the Y terminal says to connect either the Y, C* or 6 wire. Does that mean the blue wire?

Thanks for your help.

Quote:

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Originally Posted by normtoy

Frdbrkl,

On the original t-stat, the blue wire was connected to "C" terminal. Since there is no C designation/terminal on the new t-stat, the wiring diagram of the Y terminal says to connect either the Y, C* or 6 wire. Does that mean the blue wire?

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I don't believe so. I think the "C" they are referring to stands for Cooling (some stats used C or a number instead of Y) It sounds to me like you have a battery operated thermostat that doesn't use a common. It is also possible that this is one of those thermostats that have an artificial ground built in, and C is not needed-you'll have to read through the manual closely to determine what's going on with the common.

What model thermostat are you working with? Check out this site re: the Lux Programmable 1500.

http://www.luxproducts.com/ART/suppo..._WebManual.pdf

A hair over halfway down on the left hand side, several of the diagrams instruct you to "tape the C wire" if you have both Y and C, or if you have a motorized (analog programmable) thermostat. I don't think this one uses a neutral of C wire. Wrap the C wire with electric tape and see what happens. The worst that can go wrong is no operation.

Never mind the model no... doh! The TX9000. It makes reference to "this may be a common wire", but it doesn't tell you squat about what to do with it. Wrap it with electric tape. You're done.

Frdbrkl,

Thanks for your hints and help. Yes my new Lux TX9000 is a 2 AA battery operated unit. I also just happen to look at and notice Lux's online support link: Lux Products Corporation states in red, NOT to connect the "C" wire, but on the included paper instructions of the TX9000 I purchased from Orchard Supply Hardware, nowhere does it say that: http://www.luxproducts.com/ART/suppo...Eng_Manual.pdf
I noticed a slight burnt smell from one of the heating vents when I turned on the installed t-stat (with the C wire connected to the Y terminal). The wall socket fuse that the furnace plugs into, in the garage, did not short. Is there something else I can look for to see, that may be causing my furnace blower to continually blow, even when there's no thermostat installed? I don't know and probably doubt Lux will pay for or send someone out on this C wire miscommunication update that isn't in the installation/operating instruction paper, but appears on the support link I included above.
I just tried to re-install the Lux t-stat (without connecting the blue C wire) and when requesting heat, the fan continues to blow as soon as the plug is inserted into the outlet & the fuse box furnace lever is engaged. There is no spark or ignition clicking on my Day and Night furnace while the fan blows.
Is it time to call a professional for further diagnostics?

Frustrated but still not giving up,
Norm

Still not working? Stat is done most likely. Get another stat (or try the old one) and wire it up per our previous discussion. If you get another new stat, get a Honeywell(personal preference) or a White-Rodgers. They're much more common and are known for their controls. The fan running all the time may be due to a blown fuse. Check in blower compartment, see if there is an open fuse on the control board. Of course, shut off power prior to changing it...

And don't change the fuse with the current stat in place-that may be your dead short now and may blow the new fuse the instant you apply power across the stat. If it's purple, it's a 3 amp, if it's yellow it's a 5 amp blade type fuse. Check for 24v across Sec1 and Sec2 pins on control board. If you don't have 24v here-the transformer is toast and will need replacing (120v primary 24v 40VA secondary) or if you know how to use them, a multitap with a 24V 40VA output rating. If you have the 24 volts, remove all thermostat wires from stat and connect R and W wires together (quickly-don't let them spark) and see if the furnace comes on. If the furnace doesn't come on, we'll have to go a bit further. If it does come on and operate properly, you need only replace the stat to get back into operation.

Remember when you go to replace the stat-don't use a battery operated stat-and it's not the same as a battery BACK UP stat. The battery backup uses the batteries ONLY to retain programming memory in event of power outages. Since you have a common wire, use it!

For what it's worth, I recommend the honeywell T8000 series stats-they're great. Touch screen, very intuitive (and easy) programming, visibly sized characters, on/off backlight, the list goes on and on... they're expensive (around 135 bucks) but worth every penny.

Frdbrkl,

I took a day off from my t-stat change fiasco. The only fuse I could find was the circular one 10amp? That is screwed into the wall socket above the plug of my Day & Night 18 year old heater (model number 395BAW03680) to which I can't find any online info on.
I hooked up my old analog t-stat with the 4 wires (B,W,R &G) as originally installed and the furnace blower came on the moment I plugged in the plug. It still ran after I removed the t-stat. I couldn't find any fuses inside the furnace so I can't tell if they burned out. But I will say that when I hooked up the new t-stat 2 days ago, there was a slight burnt smell that came from one of the air vents. That was when my blower wouldn't quit. I must have shorted something but can't locate it. Could it be a shorted transformer? Furthermore, I couldn't locate the limit switch either. It looks like it may be time to throw in the white flag real soon. Wife called Sears the other day and they came out & recommended a replacement (of course) for a Carrier AFUE 80 model for $3777!
It just gets me that the furnace worked fine up until I changed the t-stat. I think I'm way over my head now and am considering a (professional) repair versus replacement.
Unless you have any other ideas for a humbled homeowner with no electrical skills, thank you for bearing with me and offering your advice which I'm sure someone with some handyman skills can follow and succeed. I hate to give up but it might be that time.