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Old 12-01-2012, 09:19 PM   #1
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Need help with furnance.


Hello,

I have a very old gas furnace (Payne 80U-19) and I'm having a problem with the burners not turning off. I just replaced the gas valve with a brand new unit so I am inclined to say that is not the problem. I believe it is either a wiring or thermostat isse.

Prior to replacing the valve, I had a contractor come out and try to get it up and running. They replacing the thermostat wire with a new wire, but other then that I'm really not sure what to make of their electrical work. At this moment, the burners will kick on as soon as I turn the valve to the 'on' position (even if the thermostat is on minimum heat setting). I disconnected the thermostat wires and the burners ceased to ignite.

Here is the current set up (non digital thermostat):

- R and RC connections have a bridge connecting them (but no wires attached, at the thermostat base)
- A white wire connected to Y terminal (at thermostat base)
- A green wire connected to G terminal (at thermostat base)
- Green wire is not connected to anything at furnace.
- White wire splits into two separate wires: a black wire that connects to one terminal on the valve, and a red wire (that leads to what I I think is a very small control board).

Is anyone able to help me sort out this wiring mess? I would appreciate it very much! Sorry for the lengthy post!!

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Last edited by k4ppa; 12-01-2012 at 09:22 PM.
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Old 12-01-2012, 09:41 PM   #2
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G-fan furnace and stat.
R-24 volts, furnace and stat
W-heat and usually a white wire, furnace and stat
Y (usually blue or yellow) cooling, furnace and stat with wires travelling form the control board in furnace to condenser for a/c as well as the common (moslty white is used as well) from the control board to condenser. Two wires on Y terminal on control board.

Can you take some pictures of all wiring? It hard to say what's going on with the wires that split. yes the gas valve receives 24 volts from the board but it shouldn't be the stat wires feeding it.

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Old 12-01-2012, 10:51 PM   #3
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Thank you for the prompt response Doc Holiday. Here are some pictures:

The bridge between R & Rc. Only wires connected are Y and G:

Here you can see the white wire connected to gas valve and a mysterious blue wire:

Another view (that red wires runs from that box to the switch in the background):

Not sure what this is (red wire from box runs to this... fan control switch?!):


Sorry for the last photo. I had it rotated properly, but Photobucket rotated it again for whatever odd reason.
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Old 12-01-2012, 11:12 PM   #4
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Looking at your wiring, your blue wire off of the control transformer goes to one side of the valve (via the black wire), and goes through the valve and continues on to the high temperature limit switch (thank goodness for small favors), by way of the top half of the switch, and then on to the red wire on your control transformer, completing the circuit.

So your system is wired up to come on all of the time.

Since this is a two wire furnace system (the hi-limit temperature switch also turns on the fan when the firebox gets up to temperature), then you only need two wires going to your thermostat.

At your thermostat, connect the red wire to R-Rc, leave your white wire where it is, and disconnect your green wire if you want to (no need to though). However, if you don't disconnect the green wire at the thermostat, then be sure to put a bit of electrician's tape on the end of it down at the furnace.

Back at your furnace, take the black wire off of the wirenut that joins the white, blue, and the white wires together. Leave the blue and the white wires connected and retighten the wirenut.

Take the black wire that you just freed up and connect it to the red thermostat wire and put a wirenut on it.

You should be good to go.

Last edited by rootboy; 12-01-2012 at 11:13 PM. Reason: Clarify....
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Old 12-02-2012, 12:40 AM   #5
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Thanks rootboy, your reply was extremely helpful.

I have the wires hooked up according to your description at the heater end. I installed a new digital thermostat and plugged in the red and white in their corresponding color-matched slots.

Thermostat and burner regulation is working perfectly... however the blower motor doesn't seem to kick in. I turned the heat on for about 1 1/2 min and the blower never started. I shut it off in fear of something overheating. Any idea why the blower is not turning on?
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Old 12-02-2012, 01:28 AM   #6
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G on the stat is the fan. It needs to be connected to the fan wire at the unit. When you turn on the fan only, not in heat or in cool but fan on only, does it turn on?
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Old 12-02-2012, 01:54 AM   #7
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Quote:
Originally Posted by Doc Holliday View Post
G on the stat is the fan. It needs to be connected to the fan wire at the unit. When you turn on the fan only, not in heat or in cool but fan on only, does it turn on?
Nope, nothing happens at all.

So I connect the green wire from the thermostat to the black wire I have marked as 'fan wire'?

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Old 12-02-2012, 02:20 AM   #8
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Quote:
Originally Posted by k4ppa View Post
Thanks rootboy, your reply was extremely helpful.

I have the wires hooked up according to your description at the heater end. I installed a new digital thermostat and plugged in the red and white in their corresponding color-matched slots.

Thermostat and burner regulation is working perfectly... however the blower motor doesn't seem to kick in. I turned the heat on for about 1 1/2 min and the blower never started. I shut it off in fear of something overheating. Any idea why the blower is not turning on?
No problem, your pictures were what made it easy!

Okay, what I would do next is to first turn the breaker to the furnace off. Then tie the two wires that you have identified as "Fan Line" and "Fan Load" together (to be precise, tie the two wires that are connected to the fan, not the two wires on the switch) and then turn the breaker for the furnace back on.

This will bypass the switch and allow the fan to run continuously (if it works).

If the fan doesn't come on, then start digging through the wiring to the fan (more photos please). If it does come on, then set your thermostat to call for heat and put a meter across the two wires to the temperature hi-limit switch on resistance and check to see if the switch makes. If the switch never closes (indicated by a low resistance reading on your meter), then the switch is bad.

It should be one or the other.

Last edited by rootboy; 12-02-2012 at 02:21 AM. Reason: clarification...
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Old 12-02-2012, 05:32 AM   #9
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Quote:
Originally Posted by Doc Holliday View Post
G on the stat is the fan. It needs to be connected to the fan wire at the unit. When you turn on the fan only, not in heat or in cool but fan on only, does it turn on?
Doesn't look like he has a fan relay. The fan limit looks to be line voltage on the fan side.

looks like a heat only set up with no fan control by thermostat.
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Old 12-02-2012, 06:34 AM   #10
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if that's a 110v fan switch, careful not to mix in control voltage, I can't tell where the fan wires are going from the limit.
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Old 12-02-2012, 12:26 PM   #11
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I will try to explain to my best extent where all the wires lead to:



- There is one wire coming from the fan (two sides). One side is connected to 'fan load', while the other one is connected to the 110v positive line (pink wire) & the white line that leads to the control transformer.

The rest of the high temperature switch is wired as follows:

- Fan line is connected to 110v negative.
- Limit load is connected to red wire from control transformer box.
- Limit line connected to other terminal on gas valve.
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Old 12-02-2012, 03:35 PM   #12
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You have no fan relay, just the fan limit. So don't connect your tstat to any of the fan wires.
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Old 12-02-2012, 04:27 PM   #13
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Quote:
Originally Posted by beenthere View Post
You have no fan relay, just the fan limit. So don't connect your tstat to any of the fan wires.
Alright, but how would I get the fan to turn on with the heat then? Right now the burners light up when heat is requested and then they shut off when the high temp limit is achieved (no fan). I wasn't around but about two weeks ago a contractor came out and had got the fan to fire up. I wish I was around so I could see how he had the wires hooked up...

By the way, I don't know if it's any help but I found the wiring diagram for the furnace:


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Old 12-02-2012, 07:27 PM   #14
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That is the job of the fan limit, the fan contacts lose when it reaches X temp and runs the fan. Either its bad, the cap is bad, or your blower motor is.
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Old 12-02-2012, 08:51 PM   #15
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Well I tweaked around with the settings on the high temp switch and I managed to get the fan to kick in about 4 minutes after the burners fired up!! There is three notches you can adjust on switch, and I'm not entirely certain what they refer to. Anyone know what the ideal settings might be?

Thank you all for your help... I've come a long way with all the inputs I have gotten

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