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  1. #1
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    172

    Coleman mobile home furnace tripping pressure switch

    Have a customer with a coleman evcon mobile home furnace L.P. gas, m/n dgat056bdf s/n980908580, i am the 3d person to work on this furnace supposedly tripping on fault code 3 pressure switch not proving at night only, during the day it works fine. First person replaced the pressure switch, original was .20"wc the one he installed is a .10"wc switch, customer said the furnace still trips the same error at night. Second person never cleaned or checked anything never went on the roof told the customer the heat exchanger was bad and the roof jack was no good. I spent 2 hours today checking everything, checked the heat exchanger from inside the combustion chamber with flashlight and mirror and also a borescope camera, checked from above after removing the blower, can find no crack/hole in the heat exchanger, went on the roof pulled the top off the roof jack thinking that had rotted and plugged the top of the exchanger, all looked good from up there, pulled the inducer assembly off and checked the wheel and the combustion air inlet for bees, no problems found, resealed the inducer assembly which someone else had removed and left a screw out and never scraped off the old caulk and resealed. I ran the furnace, cycled it on at least 12 times no problems at all, even put in the original pressure switch, no problems, measured the draft at the inducer -.18"wc before ignition, -.16"wc after ignition and -.13"wc after the blower starts. I can find no reason for this to drop out the pressure switch, possibly sealing the inducer housing will solve the problem, but has anyone else had issues with these coleman furnaces not proving pressure switches?? I was sure I would find a bad roof jack or bad heat exchanger but no luck. I have changed a lot of these furnaces every customer that has one has not been happy with the coleman furnaces and a lot of them have had issues with the pressure switch.

  2. #2
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Condensate trap is a slow drainer....

  3. #3
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    172
    This furnace is an 80% no condensate trap on this furnace, so far have not receieved a call from the customer in 48 hours so maybe it was a bad seal at the inducer housing.

  4. #4
    Join Date
    Jan 2006
    Location
    muncie Indiana
    Posts
    510
    Yep, I used to have lots of these issues when I did residential... Sometimes I would have to replace the induced draft motor and that would do it. It never really seemed like it was bad and ran under amperage most of the time. But if I replaced the pressure switch and got called back a second time for the samething.. It got a new motor and would almost always take care of it. But you could be on to something with the bad seal for sure.

  5. #5
    Join Date
    Jul 2010
    Location
    nebraska
    Posts
    1,629
    Those numbers correct? If the factory original switch was .2 and you had .18 with the inducer and a clear flue I'd say the inducer was weak.It should be opening with .13. The increase after the blower comes on sure looks like a seam on the exchanger is leaking. Does the O2 in the flue gas rise with the blower too?

  6. #6
    Join Date
    Feb 2010
    Location
    michigan
    Posts
    115
    i have replaced a lot of these pressure switches. there was a problem with a bunch of them and they make a replacement that comes with new tubing that you have to switch around

  7. #7
    Join Date
    Feb 2010
    Location
    In a boiler room
    Posts
    7,123
    Many of the DGAT models were under a recall for bad heat exchangers. Coleman pays for complete HX or furnace replacement.

  8. #8
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    172
    Thank you for the help, customer called back and said the furnace is still doing the same thing only at night, and that the blower just blows cold air which makes no sense cause the blower will not energize unitl the temp switch makes. My next step was to replace the inducer but I dont like to just change parts if I cant prove them wrong, I think it is either a weak/slow inducer or as someone else suggested a leaky seam on the heat exchanger. I checked the exchanger very well and could find no hole/leak but a leak in a seam I may not see, so I will see what I can find out about the recall coleman had on the heat exchanger, and if nothing else replace the inducer. Thanks again for the help, will let ya know if I get it straightened out!

  9. #9
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    172
    Also I did not check the O2 in the exhaust gas, didnt have a combustion analizer with me, just checked pressure with a manometer to see what kind of draft the inducer was creating.

  10. #10
    Join Date
    Apr 2006
    Location
    Ontario
    Posts
    13
    Try cleaning out the pickup point for the air switch on the venter motor. A little bit of rust goes a long way. Draw should be over.2"

  11. #11
    Join Date
    Aug 2012
    Location
    North Dakota
    Posts
    518
    check the stack for bird/debris

  12. #12
    Join Date
    Jul 2012
    Location
    Near Chicago Il.
    Posts
    125
    Edit:
    Open forum...So I need to word it differently. I'll just say the inducer motor could be dropping out intermittently. you should be able to follow where I'm going with that.

  13. #13
    Join Date
    Feb 2009
    Location
    Fox Lake IL
    Posts
    446
    Is there a exhaust fan that they are turning on over night putting the house in a negative. I would grab my pillow and camp out over night.

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