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  1. #1

    Clogged evaporator causing furnace overheat

    Re:Ten year old DC90 Keeprite NTGM 125EKA manufacturer is shown as Inter-City with aircon

    My temperature limit-switch kept popping (the one on the burner box) because my furnace was overheating. I tried all the reasonable things including checking the exhaust path for obstruction, checking the air filter and the registers. I also checked for a clogged exhaust fan drain - nothing worked.

    Then I decided to take a look at the aircon evaporator to see if it had become clogged over ten years of use. There was no service access - I had to unbend sheet metal seams to get at it.

    Looking inside I found it was heavily clogged with 'felt' (compacted dust) and it took me an hour to clean it using a vacuum line and a brush and a mirror - the stuff was pretty well stuck on.

    The furnace now works better than I can remember and the overheating is finished.

    My question - this looks like a sensible service job, to be done maybe every 2 years. If it isn't done the waste of gas and electricity (heating and cooling) will be major. What would a service tech do in such a case? I can't see them doing what I had to do!

  2. #2
    Join Date
    Jun 2006
    Location
    Richmond, VA
    Posts
    2,991
    Get a Service agreement and get the systemt serviced twice a year. If its kept clean it should stay clean. We put cleaner on the coil every year and monitoring the temperatures, a good tech will know when its too dirty

  3. #3
    Maybe you have access to your evaporators? I don't - the contractor assembled the evaporator into a pre-made plenum adapter, secured this to the top of the furnace and secured the duct above. The coolant lines and the drain line were simply punched holes, stoppered with plasticine (no rubber grommets). The only way to get at this to clean it is to pry the seam apart as I did. After winter's over I shall cut an access door.

    Tell me, beshvac, do you have easy cleaning access on all your customers' installations?

  4. #4
    Join Date
    Jun 2006
    Location
    Richmond, VA
    Posts
    2,991
    No, most new installations are done without regard to future maintenance. One of the first "repairs" we do with a new service agreement customer is address access issues and install cleaning ports.

  5. #5
    Join Date
    Sep 2002
    Location
    Northeast Ohio
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    4,855
    You have other problems. Have a service tech out and check the primary heat exchanger. Most likely he will find the the grommet rings that hold the sections together have popped. It will be easy for him to see once he has removed the coil for cleaning. Additionally. He should also inspect the secondary heat exchanger carefully. These have ends that are constructed of themal plastic and if the coil is as blocked as you say, this chamber could be damaged as well. We have done a couple dozen ICP units with this problem, usually caused by not changing the air filter but a blocked coil would give the same results. The burner box limit tripping is the clue to the problem.
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  6. #6
    Thanks Beshvac. Heaterman I am sure you may be right - that sounds like a new primary heat exchanger doesn't it? Don't think I shall reward them by buying one - I'll get a new furnace if that's confirmed. Is there a site that rates these (forced air gas) furnaces by reliability? Might tell me which make is the "Maytag" of furnaces - if Maytag is still even a name to respect these days.

    Also how can the Industry (where there are surely codes) allow installation of evaporator coils without access - this being as Beshvac says a service point that must be addressed bi-annually? I find that amazing.

  7. #7
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    how did the evap get so bad???
    no filter?
    some screwball ducting..........bypassing the filter?
    if the tech wants to see that coil.........either boroscope or peel that baby like a banana.
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  8. #8
    Join Date
    Jun 2006
    Location
    Richmond, VA
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    2,991
    Quote Originally Posted by sktn77a View Post
    You can bet your bottom dollar that a "service agreement" wouldn't include cutting and repairing the coil housing if it was a "lifetime sealed" unit.
    What's a lifetime sealed unit?

  9. #9
    Dandyme - Most of its life I used a Space-Gard 2200 style filter but this is a dusty old house. Some banana that, but I can tell you have been there.

    A clogged evaporator unit seems to be a frequent happening which, as I learn here, could be a safety issue (damaged heat exchangers due to over-heat) and it is surely an Energy Efficiency issue too - so where is the code that insists all installations give easy access for regular inspection and cleaning?

    You guys are in the industry - some of you ARE the industry - why aren't you re-writing the code?

  10. #10
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,038
    Quote Originally Posted by spottymaldoon View Post
    Thanks Beshvac. Heaterman I am sure you may be right - that sounds like a new primary heat exchanger doesn't it? Don't think I shall reward them by buying one - I'll get a new furnace if that's confirmed. Is there a site that rates these (forced air gas) furnaces by reliability? Might tell me which make is the "Maytag" of furnaces - if Maytag is still even a name to respect these days.

    Also how can the Industry (where there are surely codes) allow installation of evaporator coils without access - this being as Beshvac says a service point that must be addressed bi-annually? I find that amazing.
    You can buy a Maytag furnace.
    Beware of advice given by some guy on the Internet.

  11. #11
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    codes are written by NFPA and the manufacturers

    no coil access requirement in any code I've ever seen

    clearance-yes
    access-nope

    scoped & peeled many

    once upon a time our sheetmetal guy were instructed to make the built-up
    plenums with door that could be taken off, that was like pisssssssssssssn up a rope.
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  12. #12
    Join Date
    Jul 2006
    Location
    Virginia
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    4,901
    i would think there is a big air leak or the filter was never changed for the coil to be dirty with a space guard 2200 filter have replaced units 20 years old that were spotless that had a space guard , the coil probably needs to be pulled and cleaned and the problem that allowed it to get dirty solved

  13. #13
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,855
    I don't put access doors on any coils installations, on purpose. I do construct my plenum housings so that "I" can have the coil slid out in under 10 minutes, the homeowner, not likely to happen at all. I adhere to the philosophy of "If you don't know what your doing, don't be doing it!". As far as inspecting, tools needed, 1- screwdriver to remove the 1" friction cap and 1- Ridgid "See Snake".
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


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