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Old 12-18-2011, 11:15 PM   #46
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Furnace wiring


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whats the letters by the lugs on your unit again,didnt you say something about the white wire from stat going to the c terminal on yours?
normally red would be the 24v supply from transformer to stat/white would be from stat back to furnace or gas valve to supply power to gas valve on call for heat.
green would be the manual setting for blower to come on high side,but you only have single speed blower right?
yellow or blue would come back from stat to outside unit to supply 24v to contactor when ac was called for,but you normally dont have ac with a single speed blower.
the c or common terminal is normally used as a neutral on the 24v side of system to complete the circuit upon call for heat or cooling.
If you look at the PDF from Honeywell I listed earlier Figure 6 is basically what I have. The box in the figure called heating control is what I have but consists of the limit switch and gas valve. And these are wired in series with the thermostat to C and R in the "box". And this voltage at C and R drops to zero when I ask for heat.

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Old 12-18-2011, 11:19 PM   #47
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Furnace wiring


i inherited this computer from my buddy alexander graham bell,cant read those fancy pdf things on here!
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Old 12-18-2011, 11:24 PM   #48
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Furnace wiring


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OK. When thermostat is set to call for heat voltage on transformer output is 24.x volts give or take. Honeywell document referenced above says transformer is a 48 volt unit. And when I try and manually engage the system either via the limit switch or by engaging the contactor the voltage drops to 0.

How many wires are going to your gas valve. If it is two, does your meter read 24 V on these connections when there is a call for heat. If so and the gas valve doesn't open then..replace the gas valve!

If it is four wires, see if the two 24V lines from the transformer go directly to the gas valve, and measure those two connections for 24 V. If you get 24 V there then jumper the other two remaining gas valve wire connections to each other (Alligator clips) and if the gas valve does not open up then replace the gas valve. If the gas valve does open when when the jumper is on then remove the jumper and find out where on that circuit the voltage is broken.( thermostat, thermostat wires, limit contol, limit control wires).

I do not know what you mean when you say you are manually engaging the limit system or engaging the contractor on this furnace.?

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Old 12-18-2011, 11:26 PM   #49
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Furnace wiring


Ok. Here's a clip.
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