need a wiring walk-thru

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Old 03-13-07, 01:45 PM
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Question need a wiring walk-thru

Having trouble getting this particular furnace up and operating properly. It is an old J-Line (Moffat) furnace with a Robertshaw-Greyson gas valve. I can get the fan motor to come on in summer mode, but in winter mode the furnace when the t-stat wires are shorted does not fire up to heat the plenum. Hopefully somebody can walk me thru this, thanks...( doesn't fire up when wired into a temp t-stat either.)
 

Last edited by T.Green; 03-13-07 at 09:24 PM.
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Old 03-13-07, 01:57 PM
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From what we said, we know you have 110 at your furncae (blower).

But can you tell us more of what you may or may not get when you try getting it to come on and heat? Do you have an inducer motor that sends the exhaust gas out a PVC pipe, with your furnace? If so, does that even try to come on within about 30 seconds after you make a call for heat? What kind of ignition source do you have?, and does it try to ignite? Have you used a test meter to see if you have 24 volts at your transformer or at your thermostat wires down in your furnace?

Is your furnace a newer type one from the last number of years that has an open control board where the blower fan comes on by a timer?: If you are not sure, these boards have all kinds of solid state parts on them and little black relay boxes on them and numerous wires that plug into this control box. Or, do you have an older say 80's furnace that has the enclosed ignition control box that is plastic on the outside and and has maybe 5 or 6 different color wires that plug onto spade connectors on the outside of the box; it may be a Honeywell or White Rodgers brand, for example.

Note that when your furnace is in the winter mode, or on auto, the blower fan cannot run until after the flame comes on. Therefore there is no reason to even suspect anything wrong with the blower motor at this juncture.

I reread your OP and came back. I forgot you said the furnace was older. Is it so old it is not even a high efficiency one and has no PVC exhaust pipe, but goes into a chimney instead or metal flue pipe?
 
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Old 03-13-07, 04:34 PM
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This is an old J-Line with a low to mid efficency, with a old style chimney for exhaust. The blower or fan motor is fine, that wasn't the problem.The problem was having the gas valve fire the burners when heat is called for to heat the plenum and start the fan. A basic wiring walk-thru is all that I require. Thanks.The transformer is producing the required mili volt rating.thanks again...)
 
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Old 03-13-07, 05:06 PM
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Gas company did not come and shut off your gas, did they?

What kind of pilot do you have? The kind that stays on all the time, 24/7? If so, is it going?
 
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Old 03-13-07, 05:13 PM
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Wink

Thanks.The transformer is producing the required mili volt rating
Just what do you have there for sure millivolts or 24V and transformer??? There is no wire layout on the blower door????
 
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Old 03-13-07, 07:40 PM
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next and last

It's a Robertshaw-Greyson gas valve(7200E R) and the pilot is on all the time. Wiring info only please, as this is all that I require. A simple walk-thru to see if I missed a connection or step. I thought it was a milivolt one, but on a closer examination it is a 24v one. two leads one white one brown. only two conections available on valve too. By the way I'm a 2nd yr. apprentice gas fitter too, so no the gas isn't shut off.( just a run thru on the wiring please) The doors look like they've been replaced sometime in the past, before I got this old girl.(no schematic on these doors)
 

Last edited by T.Green; 03-13-07 at 09:22 PM.
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Old 03-13-07, 10:06 PM
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Ok lets try 110V to the furnace now you have the fan control and a limit control. The fan side wire hot 110V B wire through it to the blower so when temp is hot will turn the blower on.
The limit control you can wire it 110V B wire down to the in-side of the transformer. This is so if the furnace gets to hot. The limit will turn off the transformer and that will turn off the gas valve.
Now one side of the transformer 24V goes to the gas valve
The other side goes up to the tstat then comes back down to the other side of the gas valve.
Draw it out on paper first and you will see how it works
 
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Old 03-14-07, 01:27 PM
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Smile Thanks Ed

After wiring it in the way you explained it and also trying to just short the t-stat to make it call for continual heat, I found I was getting no where so I then tried another old limit switch I had lying around and what do you know she now works just fine. thanks again.
 
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