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Old 10-31-2012, 08:44 AM  
om55
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has anyone checked the heat anticipator on the thermostat, if it isn't set right it will make the furnace short cycle.



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Old 10-31-2012, 11:45 AM  
Wuzzat?
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Quote:
Originally Posted by kleinbiker1 View Post
I snaped a few more pictures before I left for work...

The disconnected white rodgers module....
Evidently your gas is ignited by other means than this high voltage module.
While you're at it, check the resistance between each of the three module terminals, T1 to term stub, T2 to term stub, T1 to T2.

Use the number of wires into each module (four wires and two wires) and the colors of the wires into each module and the larger wiring diagram that shows colors
to figure out what these modules are.
The color code abbreviations are in the lower right corner of the wiring diagram.
If the terminals of the modules are marked with tiny letters or numbers, mark these on a copy of the wiring diagram.
Temporarily unbundle wires if you need to, to trace them.

You can check the anticipator resistor with an ohmmeter but the voltage from the 'stat will tell you if the 'stat is commanding this short cycling.


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Old 10-31-2012, 01:03 PM  
kleinbiker1
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Yes the furnace has a standard old school pilot light.

I can't imagine that the stat is causing the shut down. It's the old school round dial type.

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Old 10-31-2012, 02:21 PM  
Wuzzat?
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Originally Posted by kleinbiker1 View Post
Yes the furnace has a standard old school pilot light.

I can't imagine that the stat is causing the shut down. It's the old school round dial type.
I'd try to find out what gas valve you now have.

The ladder diagram in that area has changed so I strongly recommend you draw a new wiring and ladder diagram based on what is actually in your furnace and then measure some voltages.

Your thermocouple voltage output to the gas valve can be 12 millivolts to 400 mV when connected to the valve's solenoid and twice that when the 'couple output is open circuited.
The 'couple might be bad.
You can simulate the 'couple output with a 1.5v battery and two resistors, values to be determined to see if the valve remains on.

You can probably test your old HV module by putting 24 vac into it and seeing if you can make a spark jump over a short distance. I'd hold the wires with plastic or wooden clothespins.
If the module is bad I'm not sure why the tech didn't just replace it.

Evidently the stubby terminal in the second photo of your second post was supposed to have a heavily insulated wire, like a spark plug wire, running from it to the HV module.
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