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  1. #1
    Join Date
    Aug 2002
    Posts
    490
    yes Went out on a service call today
    york furnace model P1XD12N06401
    BTU/HR INPUT 80,000 BTU/HR OUTPUT 64,000
    PROBLEM:
    furnace fires up, after two or three minites high limit open.
    even gives fault code for high limit four blinks.
    checked air flow the homeowner don't have a filter can see next room when i look up in blower compartment.
    evap is on the bottom below the heat exchanger
    took high limit out of heat ex changer, ohmed it out when it cools it closes, hot opens.
    could this be a faulty limit or em i over looking something,
    limits go like this look like working normal but faulty?
    well monday going to pick one up.

  2. #2
    Join Date
    Mar 2003
    Location
    North St Paul MN
    Posts
    858
    Originally posted by TheDuke
    evap is on the bottom below the heat exchanger

    Didja check the evap to see if it's dirty/plugged?
    I'd rather have a bottle in front of me, than a frontal lobotomy.

  3. #3
    Join Date
    Aug 2002
    Posts
    490
    no I did not but that would cause limit to open that fast 2 or three minutes, dam maybe tomorrow i should go back its late now like 5pm here in jersey I took the limit with me was going to get new one monday but not sure if its bad opens and closes, thought it maybe faulty.
    everytime unit went off i checked it with ohm meter was open
    the evap is comming up out of the crawl but can look in heat exchanger were i pulled the high limit maybe even get my small shop vac nozzle in there and hopefully clean it that way if it is plugged.

  4. #4
    Join Date
    Dec 2004
    Location
    Grand Rapids, MI
    Posts
    625
    If your multimeter does temperature, test thru screw hole for the high limit to measure actual temperature to determine if it's faulty.

  5. #5
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,777
    Dirty evap coil.
    Did you look at the blower wheel, is it dirty.
    You won't be able to clean the coil from the limit opening.
    Did you check the gas pressure at the manifold.
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  6. #6
    Join Date
    Aug 2002
    Posts
    490
    blower wheel is good i looked in there when i had top cover off, gas pressure is good.
    there was a tech there before me he had the limit jumped but then the limit on the blower was tripped i hit the reset botton and pulled out that jumper and watched it cycle a few x.
    but I thought the limit could be faulty to the heat exchanger but now im thinking about attempting to clean the evap thing is its in a real tight spot thats why i thought i could attempt to clean it through the hole for the high limit with my shop vac.
    any way just goes on 2 to 3 minutes then flame out and fault code for high limit, like i said everytime i checked it after went off i turned off emergency switch and checked the limit with the wire off and my ohm meter had nothing, then once cooled down got a reading

  7. #7
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,777
    The blower does run then?

    You'll be cursing the installer when you clean the coil.

    If the main limit would be defective, the limit at the blower wouldn't trip.

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  8. #8
    Join Date
    Jul 2004
    Location
    midwest
    Posts
    2,868
    Duke, I am sure you can clean the coil through the limit opening. Do you even know what the evap. coil is?

  9. #9
    Join Date
    Aug 2002
    Posts
    490
    The blower does run then?

    yes blower runs

    cycle
    call for heat inducer motor runs then the ignitor heats up then purges gas for few seconds, fires up flame senser senses flame blower is running goes out in like two to 3 minutes, gives fault code for high limit
    the burners were very dusty when i first went there i cleaned em with shop vac also inducer.
    i just hope its the switch is faulty or even the evap, thing is evap looks like its hard to get to all sealed up in there. in that tight corner of the 4 foot wide wash room.

    YES TRANE I know what the evap Coil is, just trying to not make a big job out of it, like I said its in small area im a big guy!

    [Edited by TheDuke on 03-12-2005 at 09:16 PM]

  10. #10
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,777
    Agaim, if the main limit was faulty, the the aux wouold not have tripped when the main was jumped out.

    Your going to have to open the case, and clean the coil.
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  11. #11
    Join Date
    Aug 2002
    Posts
    490
    yes beenthere your right.
    Very unlikely two safetys would be tripping, only limit on blower was tripped when i first got there, and yes I pulled wires to it and ohmed it out to confirm it was not closed, then hit the reset button on it.
    when I first walked in there, there was so much dust on the burners i had to clean it, i know no one is servicing that.
    downflow furnace in a very tight spot with little room for me to move around evap coil box comming about 8 inches up out of the crawl, what the best way to get in it to clean it hot water heater on one side wall 2 inches to otherside and wall 4 inches to back of it and i have about a 20 inch space in the front of it to wall oh and theres a washer drier in there and shelves.
    I can cut a hole in that evap box just enough to clean it then patch it with sheet metal what, would u suggest?
    easyest and fastest way, is thier such a animal.


  12. #12
    Join Date
    Jul 2004
    Location
    West TN
    Posts
    983
    Here's the path I would take...
    Make sure blower is coming on in the correct timeframe.

    Measure airflow through unit (I have a velometer to measure air speed, and I can convert that to CFM)

    If airflow is OK, I would...
    Clock gas meter (I have a chart that converts the amount of time one cubic foot of gas is used to Btuh being used)

    If btuh is showing too high,
    check gas pressure correct
    then orifice size for burners.

    If airflow and btuh is correct, check temp limit is actually seeing. If its tripping at a temp thats below switches rated temp, then replace switch. (don't sound likely since two seperate switches tripped)

    If airflow is not correct,
    Check for dirt accumulation in the return side of the furnace. Check blower wheel too. If the furnace is real clean, for the moment it will be safe to assume a clean evap... move on to check the supply registers to make sure they are all open. Leave blower on while checking supply registers and verify decent airflow out of each one (using velometer from earlier)
    If just a section of registers blow and another section don't, then more than likely it is a duct problem (i.e. collapsed 12" flex duct. that feeds half the house, plumber/termite man crushed a section of duct, duct liner glue came loose and spotter pins were not used and has a section of duct blanked off)
    If the registers are all low, then peak at the evap coil.
    Sound's like the evap is real hard to get to, rulling out all the other stuff might be faster than just peaking at the evap coil.
    We dont' have alot of York units here, but I have run across one doozy of a downflow furnace that had a V coil under it. Had to recover the freon, cut the lineset, slide the coil out of the cabinet, then inspect it.
    Not sure what coil you have, but from what I remember, the York coil I seen had wide spaced fins making it a bit harder to get dirty. Thats another reason I'd hold off on condeming the evap coil.

    If It looked like it was liner fallen, I'd pinpoint it by taking static pressure readings along the ductwork.




  13. #13
    Join Date
    Feb 2004
    Location
    southern illinois
    Posts
    5,536
    seems like a basic temp. rise reading would tell a guy alot....

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