Trane XE 90 pressure switch

Discussion in 'HVAC' started by eddie, Feb 24, 2006.

  1. Feb 24, 2006 #1

    eddie

    eddie

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    I have what I have found by searching other forums is a fairly common problem with a Trane XE90 furnace, I get a code when it dose'nt ignite (3flashes of a led) that shows the pressure switch is stuck open. Some times the furnace lites fine with no problem. Other times it will run the exhaust blower and start the igniter and drop out before the gas lites. Sometimes the exhaust blower will run and run and finally it will ignite after many minutes. There seems to be no pattern to it. Suggestions in other forums have been possible water in the system, clogged vent, locked up rotor in the exhaust blower. I have checked all of these with no luck. Since it happens sporatically I am sure it could be hard to determine the cause. I have a friend in the HVAC bussiness and it has him stumped.
     
  2. Feb 25, 2006 #2

    Aceinstaller

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    Air switch troubleshooting checlist......

    Plugged flue (bird nests, etc.)

    improperly sized flue (see installation specs)

    plugged pressure switch tube (remove from air switch, and inducer assembly to clear. then take paper clip and clear connection for tube to inducer assembly. replace tube and call for heat.)

    lack of combustion air causing negative pressure in utility room (ensure utility room has proper access to cumbustion air required for make and mark of unit.)

    improper low voltage readings for proper operation of air switch. (check electric diagram for proper votage, and see if the voltage at the air switch matches.)

    improper voltage at inducer motor. (check diagram for proper voltage, check voltage at motor to see if matching.)

    dirty inducer blower wheel. (rare occurance, but worth looking into last) Once I found a mouse that made his way all of the way down the flue into the inducer housing.

    If all of these checks are passed, then you have a rare occurance of an air switch going bad.(replace it):eek:
     
  3. Feb 25, 2006 #3

    eddie

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    Thanks for all your information. I am sure the flue is clear as the exhaust fan puts out a lot of air. I don't know what Trane specifies but the vent I.D. is 2 inchs which matches the exhaust outlet. It is about 35 feet long.The blower motor run freely. and the tube is not plugged up. You can gently blow or suck on the hose and hear the switch click. .I will try to test voltages as you suggest. As I said sometimes it works with no problem and other times it clicks on and off many times before it will finally light. I only recently realized that this was occuring but as I think back I believe it has been happening for several years. Thanks again.
    Also the furnavce is in a large basement so combustion air should not be a problem.
     
  4. Feb 25, 2006 #4

    Aceinstaller

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    if you blew down the tube into the switch, you might have ruined it. hence these diaphrams inside the switch are extremely thin and easily broken with too much pressure.

    My recommendation was to clear the connection at the inducer assembly with a paperclip. But I guess I should have mentioned WARNING DO NOT BLOW INTO OR INSERT FOREIGN OBJECTS INTO PRESSURE SWITCH AS IT IS VERY FRAGILE.

    Also, 2" vent piping should be increased to 3" after a specific length which is determined in a vent table that comes with the installation instructions of the furnace. I can't stand the attitude that a few bad apples in this industry have.("who needs instructions?") It seems to me that every year there is something different recommended by our manufacturers to perform on a unit for proper operation and efficiency that is overlooked by some installers.

    For a distance of 35 feet, you should replace that 2" flue with a 3". Having it installed with a 2" pipe for a long period of time put quite a bit of sress on your inducer motor as well as the pressure switch. After replacing the flue, don't expect these parts to last forever.
     
  5. Feb 25, 2006 #5

    zander

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    It sounds a lot like two problems to me.

    It could almost anything associated with the drain, flue, inducer motor, pressure switch.

    Well step one at this point would be to replace the pressure switch now that you have subject it to pressures it is not designed for. I would do this mostly for safty reasons.

    Has any one used a magnehilic or monometer or electronic monometer to figure out what the pressures in the system are? This is nessessary because without this information you are guessing away at what the problem may be. Mabey an educated guess but none the less.

    How old is this furnace? Age tends to point to the most likely part to fail.
    Im not super familiar with tranes but some times the pressure switch circuit is tied into the high limit circuit and the fault code covers both issues.
    I would check out that flame sensor too. Easy to do and eliminates it as an issue. I don't know if that train circuit board has a specific fault code for it.
    I would also think about temperaly making it a singe pipe unit.

    Worst case senerio is that you have a hole, crack, seperation in your heat exchanger and the switch won't make because the inducer motor can't work against that. Secondary heat exchanger could also be plugged up.
    Someone familiar with condensing furnaces needs to show up with the correct tools.

    I can't spell but i can think clearly.
     
  6. Feb 25, 2006 #6

    Aceinstaller

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    Yes,

    using a monometer would be the most proffesional way to determine if the inducer assembly is pulling enough pressures.

    zander, Have you ever heard of any products vent tables carry 2" pipe for 35'?

    I know that that is a undersized flue. period.;)
    and an undersized flue is the biggest reason for this problem. Just to bring the installation up to specs for it's intended use, I would replace the 2" with 3" and then troubleshoot.
     
  7. Feb 25, 2006 #7

    zander

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    Yup, seen plenty of vents that where per manufactures specs 2" and well over 35 feet. Brand has much to do with it. A 40,000 btu furnace could have a vent pipe 2" dia and 60 feet equivelant length.
    A 120,000 btu furnace probably needs a 3" pipe to be corect per manufactures guidelines regaurdless of the length.
    You could spend alot of money and time changing out that flue and it turns out to be nothing to do with the flue. AND, even though, it may be under sized it could have nothing to do with the issue at hand.
    Your going to have to pay someone to trouble shoot it most likely.
    I would seek someone out who is willing to stand behind their work. ie, not charge you for everycall when they can't figure it out.
    Let us know what it turns out to be Eddie.
    Ive heard Kentucky is high on the DIY hvac and low on the professional.
    Could be a conection there. Good luck
     
  8. Mar 1, 2006 #8

    eddie

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    I'm not sure but I think the problem is solved. It has worked OK since Saturday
    Feb. 25. I noticed a sag in the vent pipe of about 2 and a half inches in the last 15 feet from where it exited the house. It is run thru a side wall. I mounted the pipe solidly in line with the pitch of the rest of the pipe and the furnace has come on correctly every time. Keeping my fingers crossed. Thanks again to all who gave advice.
     
  9. Mar 23, 2006 #9

    dave_borchert

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    I temporarily solve this problem by removing the tube connecting to pressure switch to the combustion chamber and poking a wire through to clear out accumulated mineral ash that is obstructing the narrow nipple. This appears to be a design problem with the furnace, since the HVAC company that installed the furnace is unable to solve it.:mad:
     
  10. Mar 25, 2006 #10

    Aceinstaller

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    do not stick any foriegn objects into the pressure switch or blow into it either. only clear the inducer assembly with paper clip.:)
     
  11. Jun 6, 2006 #11

    glennjanie

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    Ah-Ha, a 2-1/2" sag in the flue line. That is a plumging problem on a "condensing" furnace; with that much sag the water had him cut completely off.
    Glenn
     
  12. Oct 14, 2006 #12

    scott

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    I awoke this morning to a FREEZING house...my furnace had stopped working. The blower kept cycling on for about 30 seconds then off for about a minute. I investigated to discover the diagnostic light flashed 3 times when the furnace was supposed to be on. A search for "trane xe90 pressure switch" brought me to this thread.

    After reading Aceinstaller's checklist that it might be related to my flue (which I doubted), I thought I'd check anyway. Sure enough, a wasps nest had been created sometime over the summer just inside the 3" PVC pipe on the outside of my house...large enough to block 80-90% of the exhaust air. How it affected the "pressure switch", I don't know...BUT, removing it solved the problem and my furnace is working again.

    Just want to thank everyone here for not only saving me the expense of a service call but the discomfort my family would have experienced while waiting for it (temps hovering around 0C/32F last night).

    ...off to purchase some wire mesh!

    Cheers.
     
  13. Oct 16, 2006 #13

    Ponte

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    I also have a Trane XE90 and I've been dealing with this problem for the last month. I think it is time to replace the pressure switch. How does one go about doing that? Is it a DIY fix or does it require bringing someone in?
     
  14. Feb 4, 2007 #14

    novice

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    I have a Trane XE 90 furnace which is in the second heating season. I've just recently had the same problem with getting the code flashing 3 times. After having someone not associated with a Trane dealer troubleshoot my furnace, and finding no problem with any of the usual switches or diaphragms, we were at a loss, thinking the problem must be in the circuit board when we discovered the problem. The problem was with a connecter at the upper left hand side of the circuit board not being completley snapped in place on the left side. It had been arching and had finally got to the place where it wasn't able to make contact any longer. It looked as though it had never been completly seated from the factory. It seats on both sides and is fairly robust in it's seating as it took a little effort to get it to snap in completely. After cleaning the contact of both the male and female at the far left side of tne connecter and putting everything back together, I've no other problems and the furnace is working fine. I don't know if this will help anyone, but just thought that I would let everyone know of this possibility.
     
  15. Nov 20, 2008 #15

    lputnam

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    Had the same exact problem. Three flashes on the LED (pressure switch problem) . Pulled off the tube on the furnace (not the pressure switch) and there was a clean white spider web completely blocking the hole. I pulled that out with a paperclip and behind it was a dead spider. Could not see this until removing the tube. All is 100% working again. Thanks for saving me about $250 in a service call and the replacement of a pressure switch that was indeed working just fine.
     
  16. Jan 11, 2009 #16

    MrMiz

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    Ok I know this was posted in 2006 and it's 2009 now but I wanted to toss my 2 cents out cuz this saved me more than $100... oh and bob villa sucks! Bob if your reading this you need to hire ME as your DIY guy. Why because I have absolutely no qualifications and I fixed this myself! Even though your web site thought I needed to spend a lot of money. I can hardly spell yet I fix problems like this. You do not want to get me started on how much I hate Professionals thinking they are the only ones in the world that are capable of working on anything.

    Anyway lets break it down.... I had flying ants this last summer. They get into everything. Down exausht vents into tubes that lead to fancy pressure sensing devices. I vacummed up what I could. I pulled off the tube to the sensore and crunched up and cleaned out the dead flying ants. Used a paper clip in the small sensor part as recommend by this web site.. I think I looked at a lot of sites and bingo no more 3 flashing light errors. Furnace kicks on and MrMiz's buns are toasty!

    My after thoughts. LEARN basic SAFETY measures and you can do and tinker with anything! Oh yah and this site rocks and you genious out there that give me the info. You rock even harder.... my socks have been rocked.
     
  17. Jan 12, 2009 #17

    glennjanie

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    Welcome MrMiz:
    We are happy it worked out for you; now you can give advice to anyone with 3 blinks!
    BTW, It takes a very narrow minded person to spell a word only one way.
    Glenn
     
  18. Sep 1, 2009 #18

    manofsteel084

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    All the information is great. Problem is, I have no idea what hoses to pull off and check. Can't find a diagram anywhere. I am getting the three blinking lights and the small box on the black fan is heating up so I shut everything off. Any help with diagrams or "how to".... is GREATLY appreciated.
     
  19. Oct 24, 2009 #19

    Jimm Two

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    All this information was very very helpful. I also had this 3 flashing code; I followed the steps recomended here.
    What i found was on the exhaust out side there was a course screen to prevent birds from getting in, but on the intake there was nothing .
    Found at the entrance to the furnace ( on the intake side) a wasp nest plugging off the air from comming in. I cleared the intake completely and put a small screen mesh over the opening to allow lots of air but with little or no restriction. Pushed the run program and the furnace was working.
    Thank you guys for all the help this was great. Jimm
     
  20. Nov 30, 2010 #20

    Bubba123

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    Just signed up to the forum to thank everyone for saving me a bunch of money!

    On a Trane gas furnace TUE unit we got the same three flashes which indicates the pressure switch. A/C guy brought out a new unit and still no dice. We checked all hoses/exhausts and everything looks good. Read this thread at the same time he is doing all of this.

    At this point he is convinced I need a new board.

    Can we just try to re-seat all connections etc.?

    "Sure, he says - might as well try".

    Wouldn't you know... unit comes right on. We put the old switch back in and e-voila, everything is still working!

    A/C guy didn't even charge me for the trip or anything. (I still tipped him.)

    THANKS ALL!!!!!!
     

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