Trane XE 90

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  #1  
Old 11-05-11, 09:25 PM
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Trane XE 90

Today I was in the basement and thought I heard a low hum for about 2 seconds that sounded like a motor trying to start but I couldn't tell where it was coming from. The washing machine and dryer was running upstairs so I passed it off as one of them just vibrating through the floor.
Tonight was I downstairs again and heard it a time or two and then the exhaust fan on the furnace came on and I could tell that was the motor I was hearing except this time the motor came on completely. After just a few seconds of the exhaust fan running the circulation fan came on. The furnace hadn't ran, the furnace was not warm at all so there was no heat in the furnace to tell the circulation fan to come on.
The glow plug never lit up and the furnace never lit. I went upstairs to check the thermostat and it was set on 68 and the temp was 68.
I turned the furnace off by the thermostat and it would not stop the fans. I turned the disconnect off and after it awhile I turned it back on and all was well but after a little bit I heard the low hum again so I just turned the disconnect off.
One note but I don't think it has any bearing, I installed a programmable thermostat about two weeks ago and it has been running fine since. It is a Honeywell and seemed to be working fine. Only four wires that were color coded so they were easy to hook up.
Any ideas? I don't know much about furnaces and will wait for a service man on monday but if it is something simple I will tackle it.
Thanks in advance for any help with this.
 
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  #2  
Old 11-06-11, 12:14 AM
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Take the cover off the burner compartment of the furnace.

Turn the thermostat way down and give the furnace a chance to shut off. Have some turn the thermostat up to 80 and carefully observe and report the sequence of events you see happening at the furnace.
 
  #3  
Old 11-06-11, 05:17 AM
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I will do that but here is some more news in the mean time...
The fans will not shut off by using the thermostat, only the disconnect.

Last night I turned the thermostat off and the disconnect on, it never tried to start (at least before I went to be after 1 AM. This morning I get up and the fans are running but no flame. I turn off the disconnect to stop the fans, I then turn the thermostat on and go back and turn the disconnect on and the furnace starts as normal. The exhaust fan comes on, the glow plug comes on, the gas valve opens and flame ignites, after a short period the circulation fan comes on.
At this point I think it will at least run one cycle since it has started but after about 10 mins (the temp had to go from 65 to 69 to satisfy the thermostat) I check and the flame is not on but the temp is only at 67 so the thermostat did not tell it to shut off.
I check the blinking light and am getting 5 flashes which says
"Flame Sensed with Gas Valve Off"
Is there a way to test the sensor? Which is the sensor? Up top in the furnace I can see what I am pretty sure is the ignitetor and more out front is what I think is the flame sensor, it looks similar to a diode setting up in space with two wires running to it. I ASSUME that is the flame sensor. Is there any way to check it?
Thanks.
 
  #4  
Old 11-09-11, 08:01 PM
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It was the flame sensor, cleaned the carbon/crud off of it and all is well.
Thanks for all the help.
 
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