Trane XL90 shuts on and off rapidly

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  #1  
Old 02-19-04, 05:35 PM
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Trane XL90 shuts on and off rapidly

Exhaust fan comes on normally, gas valve opens, it lights, it shuts off the gas, sometimes the main blower comes on when the gas is off, gas comes back on, it lights, gas shuts off, and so on. I cleaned the flame sensor with steel wool and it didn't change anything. Filter was changed a few weeks ago. I removed the filter to see if that made it stay lit longer and it didn't seem to change anything. Any ideas? Thanks so much for your help.

Mike (and Emily)
 
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  #2  
Old 02-20-04, 06:19 AM
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Souds like it may need a new igntion control board.

Sure wasn't the HSI that you've cleaned?
 
  #3  
Old 02-20-04, 09:48 AM
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Trane XL90 shuts on and off rapidly

Trane XL90 shuts on and off rapidly

Exhaust fan comes on normally, gas valve opens, it lights, gas shuts off, sometimes the main blower comes on when the gas is off, gas comes back on, it lights, gas shuts off, and so on. I cleaned the flame sensor (I think that's what it was) with steel wool and it didn't change anything. Filter was changed a few weeks ago. I removed the filter to see if that made it stay lit longer and it didn't seem to change anything. Any ideas? Thanks so much for your help.

Mike (and Emily)
 
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Old 02-20-04, 11:25 AM
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Hi
I assume you're talking about the ignitor -- that isn't what I cleaned. I read on one board that this problem is extremely common, and that there are several possible culprits. I'm pretty good with a meter -- anything I should try before calling a tech? Also, someone suggested that water in the exchanger might be causing this. Can anyone explain how that would make this happen? I'm having trouble visualizing it -- where would the water come from, etc. Thanks for any help.
Mike (and Emily)
 
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Old 02-20-04, 01:13 PM
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If you have a meter, and good with it.. Put it on the pressure switch to see if it stays close the whole time (0 volts reading), if it opens up (24 volts reading) then you will have to check to make sure the vents are clear. As for water, there should be a tube on the bottom part of the main area of the furnace, pull that out, and see if there any large amount of water there.
 
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Old 02-20-04, 03:04 PM
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Thanks Jay
How do I find the pressure switch? I just turned the furnace on after having it off all day and it ran for around 5 minutes and then the gas shut off again. Sometimes the gas shuts off within seconds of opening, and other times it stays open for a while. I can hear the exhaust fan changing speeds at what appear to be random times. (demonic possession?) Ideas? Thanks.
Mike
 
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Old 02-20-04, 06:28 PM
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Mike,

Pressure switch are going to have a couple of wires going to it. Along with some small 1/4" hose.

I can hear the exhaust fan changing speeds at what appear to be random times
Now that you are saying this.. I bet the fan speed isn't up to full speed, and cause the pressure switch to fall out. So put your meter on the switch to see what reading you're getting.
 
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Old 02-20-04, 07:58 PM
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Thanks Jay
You're right. I jumped the top pressure switch and it kicked the inducer fan into high speed. But then it dropped back down and the gas went out again. The gas went out even before it dropped back down one of the times I was experimenting. Any ideas?

Also, can you briefly explain how to use my meter to check the pressure switch. I have one of those multimeters with lots of settings. What do I set it to and how do I hook it up? Thanks for the help.
Mike
 
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Old 02-20-04, 08:24 PM
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Hey Jay
The plot thickens a bit. I took the metal cover off the board and the plastic covers off the relays because I heard a strange buzzing sound from time to time. One of the relays isn't working right -- a little sparking here and there, causing the inducer fan to slow a little here and there. Now, before I get my hopes up, is it possible that there is a different problem, or does it sound to you like if I fix the relay (or replace the board) it'll probably keep the pressure switch from opening and it'll be fixed? Also, should I try to solder in a new relay? Or is that too difficult? Thanks for your help.
 
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Old 02-21-04, 04:07 AM
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Set your meter to 200 volts AC scale.

Then put the probes on on lead on the pressure switch. (one on one, and other on the other one) Then take your reading.

Are you able to trace where this wire come from and go to? Look on the backside of the blower door, and should be a drawing on the system's wiring. That should help you trace where what go to where.. ect.

As putting a new relay on the board. not worth the hassle and all.. Just replace the whole thing..

I would get someone in if you are not able to trace the problems off hand.
 
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Old 02-21-04, 06:23 AM
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Thanks Jay
I'll let you know what I learn.
 
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Old 02-21-04, 07:19 AM
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Okay, I did the voltage test on the pressure switch and got a continuous 26 volts, as it cycled through gas on, gas off, etc. Then, after the gas kicked on one time, I jumpered the pressure switch and the inducer fan kicked on a higher speed, and the gas stayed on. Once I removed the jumper, the inducer fan idled down a speed and the gas shut off. Diagnosis? Is it the pressure switch? I thought these "never" went bad. Or could it still be the control board?

Also, is there a way for me to test the pressure switch itself?

Thanks a lot for your help!
 
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Old 02-21-04, 08:34 AM
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ok, I have not been around a 2-speed fan.. is this furnace a varable speed system?

if the pressure switch is reading 24volts all times. then the switch is not dropping out on you.


I would replace the board.. but you been going awhile with out heat?? i would call someone on Monday and get it over with.
 
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