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  1. #1
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    Confused Luxaire furnace has me stumped

    I'm looking to see if anyone has any advice or suggestions on where to go next with this luxaire furnace, it's a acclimate 9C, so originally we got called for no heat and when we got there to diagnose it the HSI would light up and the gas valve would click but no flame ever came to be, so I checked the gas pressure on the inlet side and had the proper 7" w.c. I ran the furnace again with my monometer attached to the working pressure side and the HSI lit up and the gas valve clicked but I never got pressure so naturally I replaced the gas valve and I did the collector box at the same time( it was the old clear ones that cracked and had the warranty on it) so after those 2 things were replaced and I tried to test run the furnace and it never got passed the self check phase where it tests both the pressure switches and I kept getting the error code (2 red flashes) for pressure switch stuck closed. So I thought it was just a coincidence that the pressure switch died at the exact same time so I replaced both of them the .20 and the .67 still nothing never gets passed the self check phase and throws the same error code, so this being the model with a transducer switch with runs with the .67 pressure switch, so I replaced the transducer switch and then test ran the furnace and nothing happened I'm at the exact same spot with 4 new parts, so I can make it work if I wait thill the venter motor ramps down and I pull the hose attatching the transducer off and put it on again forcing the venter motor to ramp up and complete the call for heat, but this only lasts a short time and then the heat cuts out with a (3 red flash) which is pressure stuck open, so again I can by-pass that if I pull the hose off the first time to get the flame on and then once the flame comes on and the venter motor starts it's wind down to 85% I pull it on and off again and then it will complete its heat cycle but cannot start again ! I'm hoping someone has had this problem and if I should replace the venter motor next, I just want to be sure that's the issue, sorry if it's a little all over the place but that's the problem as detailed as I could explain it my boss in 40 years has never heard of this so I'm hoping someone has some insight,

    just to add i checked the intake and exhaust pipes both were clear and well within there allowable range
    also checked the drain its clear
    also checked the board for any burn marks and water damage but it looks like its in good shape
    tried keeping the high voltage and low voltage wires separate and nothing,
    it just doesnt make sense to me to be the venter motor because it would get passed that stage before with the old gas valve,

    thanks in advance for the help

  2. #2
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    Do the differential pressure switches have a hose leading to the gas valve?? Some use the pressure to adjust the gas manifold pressure and create ideal combustion.
    There can also be debris in the orifices of the pressure taps & possibly in the cold end header box oriface (sometimes a Spider Web or cocoon). What is your differential pressure?? It sounds like you've been changing parts but not checking that pressure which is extremely important. Is the condensation trap dry or did you prime it?? To test differential pressure you'll need a dual Port manometer, some extra tubing & barb fitting t's. I prefer brass, as I've had plastic crack

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  3. #3
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    hedrash thanks for the reply

    there is no hose from the gas valve to the pressure switches, there never has been so its not something I'm missing, the switches are new so there should be no debris in the orifices, I've also taken all the hoses out made sure they were free of debris and moisture, yes they were replaced because thats what the flash code read and it made sense and thats the usual fix... ill have to get back to you with the differential pressure, but yes the brand new collector box was primed before testing and i also tried it drained, made no difference, ill get back with the pressures but thanks for the help !

  4. #4
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    Quote Originally Posted by Puksley View Post
    hedrash thanks for the reply

    there is no hose from the gas valve to the pressure switches, there never has been so its not something I'm missing, the switches are new so there should be no debris in the orifices, I've also taken all the hoses out made sure they were free of debris and moisture, yes they were replaced because thats what the flash code read and it made sense and thats the usual fix... ill have to get back to you with the differential pressure, but yes the brand new collector box was primed before testing and i also tried it drained, made no difference, ill get back with the pressures but thanks for the help !
    I was thinking the orifices on the ID fan motor, cold end header box CAI orifice. Usually a single thermostat wire can pop something out. Generally it's cobwebs or bits of PVC because the installation company uses a sawzall to cut the pipe & doesn't debur it very well. You'll be surprised. How's the venting?? Length, number of elbows, concentric, standard, flush mount?? Roll a spaldeen racquet or golf ball down the vent.... that works well for checking for obstructions.

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  5. #5
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    Collector box gasket seal is leaking or ventor fan gasket is leaking. Check pressure with manometer.

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  7. #6
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    could be a heat exchanger problem. its easy to read pressures with digital manometers but a analog magnahelic could detect issues not noticeable by digitals also if nothing is actually wrong mechanically ide suspect a connection of the control board itself. nothing has to be visibly wrong for a control board to fail as I'm sure you know. I think last year the majority of pressure switch issues were related to control boards. but do your due diligence this was brand and vintage specific....

    it is worth noting if you never performed a differential test on a draft pressure switch do not add them together as you would TESP subtract the smaller from the larger for nameplate comparison.

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  9. #7
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    Quote Originally Posted by jtrammel View Post
    Collector box gasket seal is leaking or ventor fan gasket is leaking. Check pressure with manometer.
    collector box is brand new seal is in perfect condition

  10. #8
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    Quote Originally Posted by Puksley View Post
    collector box is brand new seal is in perfect condition
    The pressure switch is not making after you changed collector box but was making before you changed it. Maybe you ran a screw in too tight and put a hairline crack in the new one.

  11. #9
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    Quote Originally Posted by Core_d View Post
    could be a heat exchanger problem. its easy to read pressures with digital manometers but a analog magnahelic could detect issues not noticeable by digitals also if nothing is actually wrong mechanically ide suspect a connection of the control board itself. nothing has to be visibly wrong for a control board to fail as I'm sure you know. I think last year the majority of pressure switch issues were related to control boards. but do your due diligence this was brand and vintage specific....

    it is worth noting if you never performed a differential test on a draft pressure switch do not add them together as you would TESP subtract the smaller from the larger for nameplate comparison.
    thought about the heat exchanger having a crack or leaking so we bypassed it as i described above and made the heat come on then did a combustion analysis and it read 5PPM so the heat exchanger is okay as well, thanks for the tip on differential pressures ! i have never done them before I've only been doing this for 3 years but have not come across a reason to do so until now, thanks again !

  12. #10
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    Those black plastic Costa Rican pressure switches are really easy to break. Sometimes they're bad out of the box.

  13. #11
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    Quote Originally Posted by jtrammel View Post
    The pressure switch is not making after you changed collector box but was making before you changed it. Maybe you ran a screw in too tight and put a hairline crack in the new one.

    i mean its possible but we took it off and inspected it for that exact reason when it wasn't working and to check the seal, also the old collector box was cracked for sometime as i could tell by the rust on the bottom plate thats the reason for replacing it in the first place and it was working with the old cracked collector box up until the old gas valve died.

    Thanks for all the help !

  14. #12
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    Quote Originally Posted by Puksley View Post
    thought about the heat exchanger having a crack or leaking so we bypassed it as i described above and made the heat come on then did a combustion analysis and it read 5PPM so the heat exchanger is okay as well, thanks for the tip on differential pressures ! i have never done them before I've only been doing this for 3 years but have not come across a reason to do so until now, thanks again !
    Get used to it.....

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  15. #13
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    Quote Originally Posted by jtrammel View Post
    Those black plastic Costa Rican pressure switches are really easy to break. Sometimes they're bad out of the box.
    good to know ! I'm kind of leaning towards the control board at this point, now because this type of furnace does a self check where it ramps up the vent motor to close the pressure switch and then ramp down to open the switch if i were to test for continuity on both switches and find they are opening and closing appropriately would that not meant the board is faulty and not allowing the furnace to start ? just a thought correct me if I'm wrong !

    thanks again !

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