Trane XR90 - Pressure Switch

Discussion in 'HVAC' started by gerrycurl21, Oct 31, 2011.

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  1. Oct 31, 2011 #1

    gerrycurl21

    gerrycurl21

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    Does the inducer create the pressure for the pressure switch to activate? How are they connected?
     
  2. Oct 31, 2011 #2

    paul52446m

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    The pressure switch is checking the pressure across the heat ex changer.
    One line goes on the drain side under the heat ex=changer, and the other go after the inducer in the top side of the secondary heat ex-changer.
    Paul
     
  3. Oct 31, 2011 #3

    gerrycurl21

    gerrycurl21

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    [​IMG]

    My furnace stop working a day ago and being completely new to hvac, everything is a new experience to me in regards to my heating. Upon taking covers off the first time, i found the 3 blinking red led which means a pressure switch error. the bottom blower works loud a well and im getting air circulation throughout my house through my registers.

    Now after clearing out the rubber hose between the pressure switch, gas valve and burner chamber i found that I can fake the pressure to the switch by taking out the chamber end of the hose and lightly blowing into it, the ignitors starts to glow red and if i keep at it, the gas valve opens and i get ignition. Of course when I stop, the gas valve shuts, ignitors stops glowing.

    I narrowed it down to gas valve (which i had to change out the honeywell valve in my hotwater tank last winter) so that wouldnt be too surprising but really unwanted. Or the inducer. When I run the furnace the inducer motor gets warm to the touch, but i cant tell if its actually running because the damn blower at the bottom of the furnace is so loud. I took off the inducer and reran everything with the inducer in my hand and the inducer is not doing anything, just getting warm in my hand. Now like i said before, i dont know anything about hvac, but shouldnt the inducer be creating air flow? either sucking or blowing through the top end? shouldnt parts be rotating as it does kinda look like a car turbo.

    Does this inducer create the pressure it needs in the hose to open the pressure switch? How would it do that if the inducer is not even connected through the rubber hose? or is inducer connected to the burning chamber?
     
  4. Oct 31, 2011 #4

    paul52446m

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    It sounds like you have found the problem, Bad inducer. Your gas valve is good. The inducer makes the pressure switch by sucking through the heat ex-changer and blows out the stack. they call all these switches pressure switches, but some work on pressure , some work on vacuum, and some read pressure difference so they use both vacuum and pressure. Paul
     
  5. Oct 31, 2011 #5

    gerrycurl21

    gerrycurl21

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    Yeah, i just picked up a new one for 250$, and the found the fins rotating on the backside of the new unit, something the old unit was not doing.

    Hopefully its a easy disconnect. I have the inducer off but its just the wiring im trying to disconnect. It doesnt seem like a simple tug and pull. Its in a plastic housing and there doesnt seem to be any moving parts on the housing.
     
  6. Oct 31, 2011 #6

    paul52446m

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    Did the new unit come with wires coming out of it? Is it possible to just cut and splice the wires back together? Paul
     
  7. Oct 31, 2011 #7

    gerrycurl21

    gerrycurl21

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    Now I just noticed on my new inducer that its missing this entire thing

    [​IMG]

    Im at work now with the part so I cant mess around with it at home to see if it still will work.

    I gave the guy at emco the part number of D342094P02 and he said that one is now superseded by a -P06 model now, which I have purchased and is in my possession.

    The new unit has the 4 wires supplied.

    3 coming from the motor on the inducer,

    -green being the ground im guessing

    -a black one with a connector i dunno how to connect

    -and a white one with a plastic connector.

    Also included is a black wire not connected to anything. One end being with the same unknown connector and at the other end being another plastic connector that fits perfectly into the other end of the white wire coming from the motor.

    [​IMG]
    [​IMG]
     
  8. Oct 31, 2011 #8

    paul52446m

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    OK. your old unit had a capasator, the new one does't. So white to white,
    green to cabinet ground. cut the black that is going under the motor and tie it to the black on the new motor. You might just have to splice them together
    Paul
     
  9. Oct 31, 2011 #9

    gerrycurl21

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    Thanks for the reply, Ill try it out in a hour or so when I get home from work.

    So the spare black wire with the new inducer doesnt get used at all?

    I will take some more detailed pics once at home of the old unit.
     
  10. Oct 31, 2011 #10

    paul52446m

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    If you look at your pic. of the old inducer , you have a circle around the capasitor where the black wire is going. see if that unplugs from there, if so you might be able to use that new short black wire to run to the black wire on the new motor. Paul Ps use caution when trying to unplug this wire because those capasitor hold a charge even when power is off. Also make sure you have a gasket seal on the inducer if there was on before. Don]t want any air leaks Paul PS It was brought to my attention,
    that i was wrong about the part you have circled in your pic. of the old inducer.
    That is a limit switch. Leave the wires on it and install it on the new inducer.
    You have a black and white coming out of the old motor, so use those to go to you black and white on your new motor.
     
    Last edited: Nov 1, 2011
  11. Nov 1, 2011 #11

    hvactechfw

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    that is not a capacitor it is a limit switch!!!!!!!!!!!!!!!!!!!!!!
     
  12. Nov 1, 2011 #12

    paul52446m

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    Glad you pointed that out, My mistake Paul
     
  13. Nov 1, 2011 #13

    gerrycurl21

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    Figured it out, pull limit switch from old inducer and transfer it over, and to remove the female ends from the old inducer, I had to take a small blade into the connector and lift a small tab up to pull out the female end.

    Everything is up and running now. New inducer creates pressure in the burner area which runs through the hose to the pressure switch. This turns on the ignitor to glow red for a lil bit and then the gas valve being connected to the pressure switch and burner area finally open allowing gas into the burner area igniting the furnace.

    Learned a shitload about furnaces in 2 days and finally got heat.

    Thx for your assistance, so glad I didn't have to replace the valve. Messing around with natural gas makes me antsy and I'd probably pay 3x as much to get it install by a tech
     
  14. Nov 10, 2011 #14

    thanksagain

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    Hi, I'm new here and don't know how to post but Ive been reading this thread,

    Someone mentioned the Open High Limit Switch on a Trane XE 90, (LED blinking 4 times) I think thats whats wrong with my unit, where is the limit switch located? There are two wires going to a sensor on the fire chamber but no reset switch, might that be it, do I replace it, just unscrew it and put a new one in? If it's not resettable.
     
  15. Oct 13, 2013 #15

    karasdad

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    Hey Paul54426M, that's not the "start capacitor" circled, it's the run limit switch and you can just remove it from the old assembly and reuse it. the black wire plugs into the white connector along with another black wire on the harness already attached. the green just goes onto the frame for ground, the white is the power that just plugs in.



    never mind, I see it's been corrected
     
    Last edited: Oct 13, 2013
  16. Oct 13, 2013 #16

    karasdad

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    it just unscrews from the inducer fan assy after you unplug the two wire plug. mine is part numbered B342017P02. I think you can purchase it from the distributor. looks like it senses some magnetic field passing by like a speedometer.
     
  17. Oct 13, 2013 #17

    karasdad

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    Thanks Gerrycurl21 for a great write up. I am experiencing a similar problem with my seven year old Trane XR90. my service guy just replaced the pressure sensor and it ran fine for a week and then started giving me the same three blinking light problem intermittently. I could trick it into working by pinching the tubes alternately. My service guy says the inducer fan assy might need replacing (D342094PO4) but suggested I clean out / blow out the tubes first. My inducer looks exactly like yours (all my sub systems are in different positions in the cabinet but look like yours). Did your inducer fan fail gradually or did it just die? There is a lot of mineral build up and deposits around the exhaust port and the drain area so I am wondering it that stuff builds up and corrodes the fan bearings and impedes performance causing my problems. I am told it is a byproduct of the combustion as is the water. It also seems to run very warm to hot, is this normal or foreshadowing failure? also did you have to use a high tem silicone sealer or is there a gasket? Thanks.
     

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