HELP! Trane XE78 cycling

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Old 10-17-09, 07:11 AM
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HELP! Trane XE78 cycling

My furnace seems to be cycling. At 68, the electronic thermostat clicks and the ignitor fires off and the 4-5 gas tubes ignite. The fan blows the heat through the registers. Then it all stops. The electronic thermostat clicks and the ignitor fires of etc... This is happening every minute or so. There are lights that blink when this is all happening which can indicate what the possible problem could be. I cannot find that doc I downloaded sometime ago to troubleshoot another problem I was having. Does anyone have a suggestion on what I need to do or look at? Many thanks!
 
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Old 10-17-09, 11:27 AM
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Probably on the ignition control module, it will identify what the number of blinks mean. See if it is printed on it. Then let us know.

It does not pay for me to go into any more detail, at this time, until we hear back, knowing you are also seeking help elsewhere.
 
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Old 10-17-09, 11:32 AM
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Too hot

I am sure you checked your filter but what you are describing is the same sequence that happens when the high limit is tripping and resetting so you might want to check air flow (closed vents or registers, collapsed ductwork, etc.) while you are waiting for further advice. The error code should be on the wiring diagram on the inside of the blower door, middle/bottom.
 
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Old 10-25-09, 03:15 AM
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Thanks for the replies.

The gas ignites in the tubes for maybe 15 seconds and then it stops. After several several times, the furnace eventually stays on like it should. It is keeping my house at the proper temperature on my electronic thermostat.

The filter is new, there are no closed vents or registers, etc.)
I found the wiring diagram, but it does not indicate on it the troubleshooting tips for the number of blinks. I pushed the button manually to see how many blinks. The light continues to blink, it never stops -- Its a White Rodgers Intel Ignition. It is literally hanging on the inside of the furnace by its wires. Do you suppose that ignition board is bad? Or there is a broken wire? I still need to figure out what is wrong. I hate to call a furnace guy if its something I can do myself.

I found this
http://site.furnacepartsource.com/pdf/50A55-843.pdf
It says on the first page- "If the light on the module is on continuously, the fault is likely to be internal to the
module" So if the board is bad -- how difficult is it to replace other that swapping the wires from 1 board to the next?

And on the Chart 5 page -- "5B" would indicate replacing the control module. I think my problem would be closely related to the "5A". I am not sure what de-energize refers to and I do not have a ohmmeter.

What are your thoughts?
 

Last edited by diychik; 10-25-09 at 03:38 AM.
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Old 10-25-09, 05:05 AM
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A constant flash would indicate normal operation. If your stat clicks with each cycle, it sounds like a stat problem.

Do you have a supply air register near the stat?

You could can remove the stat and jumper R (24volt power) to W (heat). If the short cycling stops, it's a stat issue.
 
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Old 10-25-09, 07:18 AM
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Not sure what model of t-stat you got, but if you got an older power stealing t-stat, that can make your equipment act up.
 
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Old 10-25-09, 08:55 AM
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I agree with Houston.

If the furnace stays lit for 15 seconds, the problem is probably not the ignition control. More than likely something is turning it off.

In your first post you said the thermostat would then click on (again) and the furnace would turn on ---- that suggests that the thermostat is clicking off and shutting the furnace off.

So you need to check and see if the thermostat is what is turning the furnace burner off and on, causing this cycling problem.

As Jay11 suggests, this can be caused by an improperly set heat anticipator in some kinds of thermostats.

What kind of thermostat dow you have --- make and model? Id it a digital thermostat?

If it's a conventional thermostat with a blob of mercury moving back and forth to turn the furnace on and off, take the cover off and see if the mercury movement coincides with the furnace burner turning on and off.
 
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Old 10-25-09, 09:35 AM
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Originally Posted by diychik View Post
http://site.furnacepartsource.com/pdf/50A55-843.pdf
It says on the first page- "If the light on the module is on continuously, the fault is likely to be internal to the
module" So if the board is bad -- how difficult is it to replace other that swapping the wires from 1 board to the next?

And on the Chart 5 page -- "5B" would indicate replacing the control module. I think my problem would be closely related to the "5A". I am not sure what de-energize refers to and I do not have a ohmmeter.

What are your thoughts?
What can happen today is they hand you some different control that works on many furnace models. And you have to be able to read and folow their instructions on what wires to transfer where and what jumper wire to maybe leave or remove from the new control.

If you have no actual knowledge on anything mechanical yourself, let's just say - sometimes if you know someone who kinda does, you can let them see our forum, and maybe then they could assist you, also.
 
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Old 11-12-09, 05:41 PM
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update on issue

Well to let you all know -- I ended up calling my friendly neighborhood furnace repairman. The control module is fine, however he fastened it a bit better (as it was dangling by wires) He cleaned the flame sensor with good ol' sandpaper(which I had to do last year to get it going) -- It seemed to fix the problem. It did need a thorough cleaning and he took it all apart and did so. I feel better knowing that it is done correctly and I have no worries. Just the education alone made it worth the $94. Thanks for all your imput!
~Diychik (sometimes)
 
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Old 11-03-11, 10:10 AM
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Red face Trane furnace cycles

I tried cleaning the flame sensor probe (sticks into the flame and has a white wire running from it). The sensor was clean, but realized it 'jiggled'--with only one wire coming from it to the control module I realized it needed to be grounded--sure enought, the screw holding it in place was loose. Tightened same--all is well.
 
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