Question about Carrier XHB123D X/Y Series Heat/Cool Air Conditioner

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Carrier Natural Gas Pack: Smell & Soot on exhaust tube

The heater works just fine, heats well. CO detectors (nightHawk Digital) all read 0ppm. Noticed a pungent odor outside when heat is on and there is a brown coating on aluminum exhaust vent tube. This tells me the gas may not be burning completely and perhaps increasing my heating bills. I want to open the unit to check for air inlet restrictions & clean whatever may be dirty & interfering with the air/gas mixture.
The gas pack is beside the house and easy to access, top comes off easily.
Looking for pointers on what to expect & procedures for this service.?
THank you

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  • CajunWon Dec 19, 2008

    I was able to look at the unit. turned on and the flame going into the heat exchange pipes as nice and blue and appeared to have an unobstructed flow into the exchanger. Looking into the vent with flashlight, no obvious obstruction. The heat exchanger is 'U' pipes. The outer pipe is twice the diameter of the inner pipe. The inner pipe has significant dimples, guess to increase surface area. But inside the dimple have obvious corrosion and even holes that appear almost like intentional narrow slots. These hole/slots are only on the lower portion just before the exhaust exits the unit.

    So is this inner/smaller pipe supposed to have these holes/slots?

    excuse my bad drawing here.

  • CajunWon Dec 21, 2008

    Quick search at shows a Heat Exchanger for Carrier 48SX at $578, about 5x more than I was thinking. Considering a repair/patch of this issue. Steel wool to remove surface corrosion, assuming this is rust so use a rust converter on surface to prep area. Apply JBWeld 500* to patch. These small holes are within 18" of the exhaust vent, assuming the pipe temps are less than 500*F by this point.

    If this resolves the exhaust smell & lite soot, then I've isolated the issue. After heating season remove exchanger, take to welder and let them suggest solution, perhaps to bronze/braise these small holes.

    Critique welcome



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Time for a good cleaning. Make sure the heat exchanger is in good shape and is getting good heat flow over it to the exhaust. The odor may be an indication of a restriction in the heat exchanger, the flames are hitting something, improper air or gas adjustment or a blower not coming up to correct speed. You can access the heating unit from a side panel. Look for the exhaust port and start with that panel. Wasps nests are predominant in these things.

Posted on Dec 19, 2008


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