Furnace Cycle Question


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Old 01-12-10, 08:25 PM
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Furnace Cycle Question

I have about a 8 year old gas furnace, electronic ignition, and about a three month old Honeywell manual thermostat.
The issue I'm having is that everything seems to be working good except that the furnace is shutting off very early, about 67 degrees, and then starting back up after less than a minute. I am 99% sure its my thermostat, I turned it up to 85 degrees thinking it shouldn't turn off until Im sweating, and Im getting the same result, cycling often. Im going to get another themostat tommorow hoping that fixes my issue.
The question I have is could I "cheat" or short my thermostat wiring to elimenate the themostat from the equation?
 
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Old 01-12-10, 09:00 PM
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What is the model of the thermostat?
 
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Old 01-12-10, 09:25 PM
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The model is Honeywell, CT31A. It was a cheapy.
 
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Old 01-12-10, 09:48 PM
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That is a magnetic thermostat, so it doesn't need to be leveled.


Take the cover off and see if there is an adjustable heat anticipator inside--- a coil of fine wire with a lever that can be set over it.

See if you can observe the magnetic contacts opening and closing.

If so, the heat anticipator needs adjustment.
 
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Old 01-12-10, 10:05 PM
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The Heat Antisipator, the very fine wire or filiment with 1/10 incriment adjustments? It has a small piece of copper that "rides" on that small filiment. That has been a concern, whether or not the piece of copper was making contact with the filiment or wire.
When the furnace shuts off the copper coil between the magnetic contacts is not moving from left to right, unlike it was shutting off after reaching a desired temp.
There are two adjustment screws on each side of the coil above each magnetic contact, what would an adjustment to these do?
 
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Old 01-12-10, 10:13 PM
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I can't recognize what is going on from your description.

If you have the thermostat manual, review the section that discusses adjusting the heat anticipator. It sounds like that is the problem.
 
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Old 01-12-10, 10:25 PM
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Well you still havent answered my initial question about cheating or bypassing the themostat, for troubleshooting purposes of course. Im an electronic tech by trade so Im sure I can do it, its just a matter of knowing my wiring colors; fan, heat, common, and ac. I do understand to you probably have to be careful about what you say for liabilty reasons.
 
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Old 01-13-10, 05:17 PM
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You hook together the R and W wire at the stat or in the furnace, to where you can bridge the two terminals with alligator clip wire or a piece of wire.

So you understand how this works - 24 volt current is supplied to terminal R in the furnace. Then when the stat is turned up, the current can then flow out of terminal R up to the stat, where then it makes a closed connection with terminal W, that then returns back to the furnace from the W terminal in the stat and back to the W terminal on the low voltage terminal connector down in the furnace.

Obviously - by leaving such a hookup jumpered, the furnace will never shut off. So you have to remember to put things back to as they were, when done testing.
 
 

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