Trane XE80, it is not the pressure switch

Discussion in 'HVAC' started by pookie16, Dec 7, 2011.

  1. Dec 7, 2011 #1

    pookie16

    pookie16

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    I posted a reply on another thread and did not get any response, so I am starting a new thread.
    I think I read all threads on this topic as I thought I had a similar problem. I get the three blinking lights after the furnace works for a few hours every day and I need to manually reset the furnace.
    I replaced my pressure switch and I still have the problem.
    If I shut the furnace off and turn it on, the furnace will light.
    If I squeeze the tube to the switch and release, it will light.
    If I take the tube off at the switch and put it back on, it will light. If I take it off and even just hold it close enough to get some vacuum to the switch it will close and light.
    The furnace is very new and there is no sign of any dirt or moisture anywhere.
    I replaced the switch because it seemed to me that perhaps it was sticking and needed to be opened and then closed again in order for the contact to be made. Replacing the switch proves it is not the switch. There is plenty of vacuum to close the switch, so it is nothing between the switch and the inducer.
    What else could it be?
     
  2. Dec 8, 2011 #2

    hvactechfw

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    it sounds as though the vacuum is borderline. You can not find this out for sure without a manometer. However, you need to check your flue. It may be partially blocked.
     
  3. Dec 8, 2011 #3

    pookie16

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    Thanks for the reply, but I want to ensure that the switch would work in a way that seems counter intuitive to me.
    So even though if I take the hose off and hold the hose close to the inlet of the switch and it will work every time, you think it sounds like not enough vacuum? I was thinking that is lots of vacuum if there is enough to overcome the major leak of not even having the hose totally attached. How much vacuum do I need if I get a manometer and test it? A few inches of water?
    I am not sure why it will always work if I turn it off and then on, if it was a vacuum problem. If there is an instance of not enough vacuum once, does that prevent the switch from closing until you let it open (by releasing the vacuum) and then reapply the vacuum? I will check the flue and let you know. I will not have access to the furnace for a few days as I am out of town.
    Thanks
     
  4. Dec 9, 2011 #4

    paul52446m

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    Pressure switches are used different way's. Some furnaces have two switch,s, some have one with two hoses and some have one switch with one hose. If you have one switch and one hose, when you pull off the hose or turn off the power and back on, the unit has cut out on safety and you are recycling it. You say it runes for a few hours then turn off . This sounds like the drain not working right. it builds up with water in the heat ex changer and the pressure switch turns it off. After it set for a while, it drains out and you recycle it and it starts back up. Sounds like your drain it working, but not good enough. Paul
     
  5. Dec 9, 2011 #5

    hvactechfw

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    The only problem is the title of the thread states that it is an 80%
     
  6. Dec 9, 2011 #6

    pookie16

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    I agree with this last post. At first the idea of water building up made sense. I have never seen any drains on any furnaces I have owned, and I do not see one on mine. I know it is not hooked up to the sewer system and there is never any water on the floor, so I suspect the 80% furnaces do not drain.

    So then, what else could it be? I did a test of turning the thermostat down and up to see if that cleared the error signal (those 3 flashes) but it did not.
     
  7. Dec 9, 2011 #7

    pookie16

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    And back to the low or intermitent vacuum. I agree that this could be a problem, but I still don't know why just pinching the hose would make the furnace start. If it is a case of intermitent vacuum, then the symptoms should be the same as pinching the hose (removing the vacuum and putting it back). What am I missing here? Oh and if I test the vacuum, how much should there be?
     
  8. Dec 9, 2011 #8

    pookie16

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    I tested the vacuum - 200Pa or 0.75in H20. Is that good or bad?
     
  9. Dec 9, 2011 #9

    hvactechfw

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    It depends on what your furnace pressure switch calls for. sometimes its listed on the switch, other times you have to call the manufacturer.
     
  10. Dec 10, 2011 #10

    pookie16

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    Is it possible that the pressure switch has to open at some point in the cycle? What if the induction blower stayed on sometimes when it was supposed to be off. This would not allow the pressure switch to open and then the cycle would not start. Me pinching the hose to the pressure switch allows the switch to open and then close again when I release it. Is this possible and if so, what would keep the induction blower running?
     
  11. Dec 10, 2011 #11

    hvactechfw

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    yes, if the inducer never stops running even when there is no call for heat, then you need a control board.
     
  12. Dec 10, 2011 #12

    pookie16

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    I made an appointment with some guy for Monday. The inducer does stop running sometimes. It is just difficult to sit by the furnace all day to see what happens when it stops functioning correctly. Of course, when the temperature drops, there is a already a call for heat. So it is difficult to know when the inducer was running or not.
    Thanks for the suggestions. I will post what the guy does to fix the problem.
     
  13. Dec 12, 2011 #13

    pookie16

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    That guy came and charged me $120. He set the thermostat for a longer cycle, thinks he might have cleaned the vacuum nozzle, and put a longer hose going to the pressure switch. The theory is that the thermostat was calling for heat while the inducer motor was still turning. This way, the pressure switch doesn't open and the cycle is disrupted. I am heading out of town again, so hopefully the $120 pays off.
     
  14. Dec 14, 2011 #14

    pookie16

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    It appears the $120 spent has had no impact. The wife suspects that the furnace quits more often than before the mods. My next step will be to replace the mercury thermostat with a new fangled electronic one as the guy I gave the money to suspected that calls for heat were coming too quickly while the inducer was still turning. If that does nothing, then the board will be replaced.
     
  15. Dec 17, 2011 #15

    pookie16

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    The furnace has been running without problem for 3 days now despite not changing anything. This makes me think it is the board. I am afraid to leave the house unattended in case the furnace quits again and the pipes freeze. Difficult to fix a problem without it shutting down on its own.
     
  16. Dec 18, 2011 #16

    paul52446m

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    I am a heating dealer and what i do for my customers is, for a small yearly fee, i have them put in a PH alarm with a heat censer in it that is set at 45 degrees. So when the heat in the home drops to 45 the PH alarm will call me
    and we pick it up on caller ID. We have the home owners key, so we fix it. Its a great system and i charge them $30.00 a year to be in our system.
    Paul
     
  17. Dec 18, 2011 #17

    pookie16

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    That sounds incredibly good. I will see if anyone has something like that in my area.

     
  18. Dec 18, 2011 #18

    hvactechfw

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    OR, you could get a paging system that will call YOU if the heat goes that low. and not have to pay a yearly fee. Or you could get a wifi thermostat and check your home temp online or on your phone.
     
  19. Dec 19, 2011 #19

    paul52446m

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    The reason my customers like being on my yearly program with a PH alarm is
    This is a resort area so a lot of these people are not here only on weekends.
    They could just buy a PH alarm and have the alarm call there Ph with a long distance call every 15 min. until the heat comes back up, or if they want peace of mind, they can have it call me in the middle of the night and i will take cake of there problem even if they are out of the country. My customers love them.
    Paul
     
  20. Dec 24, 2011 #20

    pookie16

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    The problem went away. The furnace has been working for more than a week now. This makes me think it is the mother board, as modern electronics is prone to doing wacky things.
     

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