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Old 12-18-2011, 10:34 PM   #31
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Furnace wiring


I know decent electrical and electronics. Just missed the VA. Too many trips in and out of crawl space.

There appears to be in series the
Temp limit
Gas switch with thermocouple to pilot
Flue gas cutoff w/ sensor next to pilot
Then back to control box transformer.

AC 120V goes to
Temp limit
Then Fan control
Then Control box

I can make the fans run either by setting fans to ON at thermostat or manually rotating temp limit wheel to fake heated air with thermostat set to heat or pushing in the solenoid in control box.

With the later two forced fan run tests the voltage out of transformer drops to 0. Which implies to me a bad secondary winding. Which is why I'm leaning to It being a bad transformer.

Or not.

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Old 12-18-2011, 10:40 PM   #32
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Furnace wiring


if you get 24v out of the transformer its good
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Old 12-18-2011, 10:42 PM   #33
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Furnace wiring


primary side of transformer is 120,the secondary is where youre getting your 24v to run the system from
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Old 12-18-2011, 10:45 PM   #34
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Furnace wiring


where are you located? if youre within 100 miles of louisville ne ill drive out there and fix it ,you just buy the fuel for truck/lunch for me and the parts!
this post has gone on way too long for something simple
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Old 12-18-2011, 10:47 PM   #35
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Quote:
Originally Posted by plummen
if you get 24v out of the transformer its good
But it drops to zero when I try and run the system. To me that indicates a secondary winding with a broken but touching wire. Or is there a reason it drops to zero?
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Old 12-18-2011, 10:48 PM   #36
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where are you getting the zero volt reading?
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Old 12-18-2011, 10:49 PM   #37
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Quote:
Originally Posted by plummen
where are you located? if youre within 100 miles of louisville ne ill drive out there and fix it ,you just buy the fuel for truck/lunch for me and the parts!
this post has gone on way too long for something simple
I used to live in Lexington but that was over 30 years ago.
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Old 12-18-2011, 10:51 PM   #38
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Quote:
Originally Posted by plummen
where are you getting the zero volt reading?
Between C and R inside the control box. (Just what do you guys call that thing anyway?)
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Old 12-18-2011, 10:51 PM   #39
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ive been to kentucky,but im in louisville nebraska!
we also have a nashville ne,about 45min north of here
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Old 12-18-2011, 10:52 PM   #40
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Furnace wiring


are you taking these readings to ground with the fan on or across the wires?
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Old 12-18-2011, 11:00 PM   #41
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I get 24 volts with thermostat calling for heat. But fans are not running.

If get the fan running by tricking the limit switch or manually engaging the solenoid then the voltage drops to zero.

Solenoid never engages by itself.
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Old 12-18-2011, 11:01 PM   #42
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Quote:
Originally Posted by raleighthings View Post
Between C and R inside the control box. (Just what do you guys call that thing anyway?)
junction box or place for low voltage connections ,terminal board i guess you could call it just about anything.
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.
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Old 12-18-2011, 11:04 PM   #43
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Quote:
Originally Posted by raleighthings View Post
I get 24 volts with thermostat calling for heat. But fans are not running.

If get the fan running by tricking the limit switch or manually engaging the solenoid then the voltage drops to zero.

Solenoid never engages by itself.
when you manually turn the dial on the limit switch the furnace is fooled into thinking its out on high limit,this cuts the power to the transformer so burners will not come back on till furnace cools down and limit resets itself
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Old 12-18-2011, 11:10 PM   #44
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Quote:
Originally Posted by plummen View Post
when you manually turn the dial on the limit switch the furnace is fooled into thinking its out on high limit,this cuts the power to the transformer so burners will not come back on till furnace cools down and limit resets itself
What I'm doing is turning it just enough to trigger the initial start of the fan. Something around 100. My understanding this is to keep from blowing cold air around.
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Old 12-18-2011, 11:14 PM   #45
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if its killing the 120v to transformer id say its kicking out on limit .
have somebody check for 120v and v depending on how furnace is wired out of other side of limit switch while you do it

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