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Old 01-20-2012, 06:06 PM   #1
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Trane XR90 - Condensate Drane Trap


I have read the posts by Tom Scott and others having the dreaded 3 red light pressure switch error. I have the same problem. Furnace runs fine with the vacuum tube from the pressure switch to the burner box disconnected, so we don't freeze at night, but of course that's not a safe long term solution!

I've cleaned all of the vacuum tube lines, nipples and connections. I've checked and cleaned the condensate line from the inducer motor and from the heat exchanger area of the furnace. I've checked that the air intake and exhaust pvc ducts are clean and clear. I've even replaced the pressure switch (twice!) and the inducer motor, which had some stains on the underside, indicating possible overheating, I thought.

After all of this, I still had the problem, so I called the local Trane dealer.

The Trane repairman spent about an hour testing and diagnosing the problem. Checking pressures and such. He discovered that if you plug the end of the condensate drain line coming from the furnace (not the line from the inducer motor), the pressure switch error goes away. He thinks the problem may be with the condensate drain trap, which is not set up properly, he says.

As you can see (I hope!) in this picture, the condensate drain lines from the inducer motor and from the heat exchanger are simply routed into a pvc drain pipe with a gravity trap built into it, like under a sink.





The pressure switch error (3 red lights) goes away if you plug the end of the condensate line that comes from the furnace (not the line that comes from the inducer motor). Repairman says Trane makes a condensate drain trap that should have been installed when the furnace was originally installed in 2003.

Note that the drain line that comes from the furnace does not extend all the way down to the bottom of the pvc trap, where it would be submerged in a bit of water. It only extends a few inches into the pvc pipe, so that air can flow backward through the condensate line into the furnace heat exchanger area right next to the vacuum line that goes to the back of the pressure switch, reducing the relative low pressure in the furnace at the heat exchanger area.

Does a faulty condensate drain trap sound like a correct diagnosis?

Does the the Trane condensate trap actually prevent air from flowing back into the furnace? If so, then problem solved.

Should not be complicated to install the trap. However, I went to the Trane site and discovered that they do not sell direct to the public. Is there anywhere that I can purchase the Trane condensate trap and the appropriate size tubing (as existing lines undoubtedly will not be long enough)?

Of course, if the Trane condensate trap allows air to flow back into the furnace heat exchange area, then problem is not solved, and all that is left is to conclude that the heat exchanger (or transition piece to inducer motor) must have cracks, as many others have had.

Thanks for any advice you may be able to provide.

JD


Last edited by JDWorks; 01-20-2012 at 06:24 PM.
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Old 01-20-2012, 06:17 PM   #2
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Trane XR90 - Condensate Drane Trap


Transition piece was a problem in 90% in 2007causing leaks around inducer area,but never effected operation. You may try making a trap with 1/2" cpvc

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Old 01-20-2012, 06:30 PM   #3
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Trane XR90 - Condensate Drane Trap


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Transition piece was a problem in 90% in 2007causing leaks around inducer area,but never effected operation. You may try making a trap with 1/2" cpvc
So are you saying that cracks in the transition part did not cause pressure switch error?

I already have a pvc constructed trap, which the Trane repairman thinks may be causing the problem.
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Old 01-20-2012, 06:42 PM   #4
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Trane XR90 - Condensate Drane Trap


The transition piece has never caused a shut down on the furnaces i have worked on. However it should be replaced . your trap is not what i was thinking. I would remove the trap you have, get a hose create a loop and then to your drain that may work.
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Old 01-20-2012, 06:44 PM   #5
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Trane XR90 - Condensate Drane Trap


the clear tube on the left gose up to a white fitting looks like its pinched closed?
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Old 01-20-2012, 06:49 PM   #6
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Trane XR90 - Condensate Drane Trap


thats NOT the trap from the factory......you may have a cold header crack on the secondary heat exchanger
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Old 01-20-2012, 07:05 PM   #7
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Trane XR90 - Condensate Drane Trap


QBert - So you're saying the trap installation could be causing the problem? FYI, I have submerged the end of the clear plastic tube coming from the furnace into water in a glass, preventing air from flowing freely back up into the furnace. That doesn't seem to solve the problem. Vacuum draws 1-1/2 to 2 inches of water back into the tube.

LayJ - The clear condensate drain tube on the left is slightly pinched, but definitely open. Condensate water is easily draining down and air is easily flowing through it.
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Old 01-20-2012, 07:10 PM   #8
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Trane XR90 - Condensate Drane Trap


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thats NOT the trap from the factory......you may have a cold header crack on the secondary heat exchanger
Harley - I understand that the trap installed is not the Trane trap. Could the trap, as installed, be causing the pressure switch error? Said differently, does the Trane trap do anything that the pvc trap doesn't do?

Thanks for your thoughts on this!
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Old 01-20-2012, 08:08 PM   #9
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Trane XR90 - Condensate Drane Trap


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Originally Posted by JDWorks View Post
Harley - I understand that the trap installed is not the Trane trap. Could the trap, as installed, be causing the pressure switch error? Said differently, does the Trane trap do anything that the pvc trap doesn't do?

Thanks for your thoughts on this!
yeah........the factory trap has two connected but seprate chambers........
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Old 01-20-2012, 11:16 PM   #10
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Trane XR90 - Condensate Drane Trap


OK, understood that the Trane trap does something that the pvc trap does not do. Where can I purchase a Trane trap? Anywhere online?
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Old 01-21-2012, 01:16 AM   #11
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Trane XR90 - Condensate Drane Trap


I suppose it's a drain trap, not a "drane" trap. Just like it's a Trane Furnace not a "Train" Furnace. Glad we got that straightened out!

Last edited by JDWorks; 01-23-2012 at 11:54 AM.
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Old 02-07-2012, 01:02 PM   #12
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Trane XR90 - Condensate Drane Trap


I have now installed a Trane condensate drain trap as shown in the picture below:



Unfortunately, we're still having the pressure switch error problem. Furnace seems to run fine with the vacuum tube from the pressure switch to the burner box disconnected (as shown in the picture), so we don't freeze at night, but if I reconnect that tube then I soon get the pressure switch error.

Trane repair technician says the only remaining possibility is that there must be cracks (air leaks) in the heat exchanger unit, and this is a big job to replace. He says the heat exchanger unit itself likely will be covered by Trane warranty, but the cost of labor to replace, about $1,500 he estimates, would be mine. Is this a reasonable estimate? Is this work typically done time & materials or fixed price?

Thanks,
JD

Last edited by JDWorks; 02-07-2012 at 01:10 PM.
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Old 02-07-2012, 01:12 PM   #13
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Trane XR90 - Condensate Drane Trap


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Originally Posted by JDWorks View Post
I have now installed a Trane condensate drain trap as shown in the picture below:



Unfortunately, we're still having the pressure switch error problem. Furnace seems to run fine with the vacuum tube from the pressure switch to the burner box disconnected, so we don't freeze at night, but if I reconnect that tube then I soon get the pressure switch error.

Trane repair technician says the only remaining possibility is that there must be cracks (air leaks) in the heat exchanger unit, and this is a big job to replace. He says the heat exchanger unit itself likely will be covered by Trane warranty, but the cost of labor to replace, about $1,500 he estimates, would be mine. Is this a reasonable estimate? Is this work typically done time & materials or fixed price?

Thanks,
JD
yes a cold header crack was mentioned in this thread, and thats been a Thorn in the side for Trane for many years now. I am not a Trane dealer, but We have done our share of these heat exchangers, we charge a Flat rate of $900. Typically they take about 3 hours to complete, and then you have a mountain of paper work to complete as well as the transportation of the heat exchanger back to Trane. Everyone has there own way of doing things, but $1500,00 does sound a tad bit high.
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Old 02-07-2012, 02:32 PM   #14
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Trane XR90 - Condensate Drane Trap


Fill trap with water, and then see if you still get the error. if you do. Your tech can use a combustion analyzer to check to see if there are signs of a crack.
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Old 02-07-2012, 03:32 PM   #15
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Trane XR90 - Condensate Drane Trap


DOSY777 - Thanks for the advice. I have another company scheduled to diagnose and scope the heat exchanger for cracks tomorrow.
BeenThere - Filled trap w/water, and still get error. Thanks for the suggestion.

JD

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