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Old 09-06-2009, 04:36 PM   #1
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Bad smell from central air unit


We've noticed a bad smell coming from our central air unit. My brother who has worked in the HVAC industry for quite a while came and checked it out thinking it was the "condensate tray" that may have something growing in it. There is no easy way to access the plenum but we were able to look inside enough to see that the tray is angled enough that my brother says it should be draining 100% and thus have nothing growing in it. The "condensate line" also appeared clear of obstructions. He sprayed some kind of a cleaning mist into the fresh air intake vent and said that should get rid of anything that might be present in the system. It didn't....lol. We still have the bad smell....any other suggestions? I'm no HVAC professional so go easy on me with the terminology....lmao.

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Old 09-06-2009, 06:04 PM   #2
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Bad smell from central air unit


What does it smell like?

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Old 09-07-2009, 09:43 AM   #3
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Bad smell from central air unit


He checked some basics, which is good. Do you have a condensate pump and/or P trap on your condensate lines somewhere? Sometimes odors can get pulled back up the condensate line - which is what a P trap would prevent, and pump maybe. Also check for a low spot somewhere in your condensate lines as it doesn't take much water for beasties and yucky stuff to begin multiplying.

Please answer beens question as this might be another issue.
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Old 09-07-2009, 10:35 AM   #4
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Bad smell from central air unit


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Originally Posted by beenthere View Post
What does it smell like?
Its kind of a "sulfur" smell. Its a propane furnace and I'm 100% certain its not a leak from there but I would characterize the smell as almost a propane smell. We had a new secondary heat exchanger put in over the winter. I just asked the wife if we had this smell before this repair and neither of us can remember if we have....

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He checked some basics, which is good. Do you have a condensate pump and/or P trap on your condensate lines somewhere? Sometimes odors can get pulled back up the condensate line - which is what a P trap would prevent, and pump maybe. Also check for a low spot somewhere in your condensate lines as it doesn't take much water for beasties and yucky stuff to begin multiplying.

Please answer beens question as this might be another issue.
There is a line that comes out at the bottom of the plenum that the condensate tray drains into.....that angles down into a T fitting and I noticed that the top of that T fitting is not covered with a cap should it be? Here is a diagram of the tubing as it leaves the plenum....
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Old 09-07-2009, 10:53 AM   #5
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Bad smell from central air unit


Have them check for a gas leak.

Ethyl Mercaptan may be what your smelling. Its the odorant added to propane so you can smell it if you have a gas leak. Could be your gas valve is leaking through. Or, a fitting is leaking.

Have it checked ASAP!!!
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Old 09-07-2009, 11:33 AM   #6
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Bad smell from central air unit


Wouldn't I smell it other times then when the central air is on? This smell is present only when the central air is on and blowing air through the register. Not to be a smart alec but wouldn't we have blown up by now....I mean my brother has been down there smoking and I've had a generator running near the door on one occasion.
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Old 09-07-2009, 01:45 PM   #7
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Bad smell from central air unit


Nope.

Need X PPM of gas for it to ignite.

The odorant is a lot stronger smelling, then the amount of gas in the air. The gas is also heavier then air. So it wouldn't rise into the house without help from another source of force to move it to there.

Your coil is on top of your furnace. So teh blower is before the coil. So I doubt your pulling in an odor through your drain lines since they are positive pressure while the A/C is running and blowing air through your registers.

It may be from something other then a gas leak.

Not to be a S. A. But.
Hopefully, you think enough of your family, to have a leak check done.
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Old 09-07-2009, 02:18 PM   #8
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Bad smell from central air unit


You mentioned that the smell occurs only when the a/c is on. Did your brother spray the coil with a bleach solution, or just spray the intake. It's possible that the funk is in the coil.
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Old 09-07-2009, 02:51 PM   #9
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Bad smell from central air unit


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Originally Posted by beenthere View Post
Nope.

Need X PPM of gas for it to ignite.

The odorant is a lot stronger smelling, then the amount of gas in the air. The gas is also heavier then air. So it wouldn't rise into the house without help from another source of force to move it to there.

Your coil is on top of your furnace. So teh blower is before the coil. So I doubt your pulling in an odor through your drain lines since they are positive pressure while the A/C is running and blowing air through your registers.

It may be from something other then a gas leak.

Not to be a S. A. But.
Hopefully, you think enough of your family, to have a leak check done.
I'll check into the gas leak scenario this week.....


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Originally Posted by Flashheatingand View Post
You mentioned that the smell occurs only when the a/c is on. Did your brother spray the coil with a bleach solution, or just spray the intake. It's possible that the funk is in the coil.
No it was all we could do to actually look inside the plenum to see the condensate tray...there was no door or any access panel left to get easily inside. It should be noted also that the smell doesn't occur all the time when the a/c is on....it tends to come and go.

Now when he sprayed the fresh air intake my wife and I both thought the smell disappeared for a while....its been cool enough here that we haven't really ran the a/c that much but when we started it up recently...about 2-3 weeks after he sprayed the smell is back. We poured a small amount of bleach into the sump pit...my brothers' reasoning was if the plenum or any of the piping is not sealed 100% tight (which it isn't) that it could be sucking up stagnant air from the sump pit or musty air from the basement as its quite damp in the basement. We both noticed the smell in the basement around the a/c-furnace and although it smells somewhat like propane...we both concurred that its a little different but still an obnoxious odor.
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Old 09-07-2009, 03:50 PM   #10
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Bad smell from central air unit


I don't know about the smell. You just mentioned how it only occurs during cooling. If so, To eliminate the a/c, I would clean the coil. You might might suggest to your brother, that pulling the heat exchanger may help with access. It's can be a pain, but if he is a hvac guy, it should be feasible.
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Old 09-08-2009, 04:25 AM   #11
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Bad smell from central air unit


Just looking at that pipe drawing, I noticed there was a tee. It's better to have an air gap. As it is, the sump smell can get inside of the furnace. With an air gap, the smell goes into the room, but not necessarily into the furnace/ air handler.
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Old 09-11-2009, 07:11 AM   #12
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Bad smell from central air unit


What is an air gap? I've suspected that it is coming from the sump pit....that water is pretty stagnant and doesn't get pumped out enough in my opinion.
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Old 09-11-2009, 08:34 AM   #13
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Bad smell from central air unit


If you're certain the odor is coming from the drain then just throw in a P-trap.
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Old 09-11-2009, 09:12 AM   #14
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Bad smell from central air unit


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Originally Posted by dac122 View Post
If you're certain the odor is coming from the drain then just throw in a P-trap.
Spray Febreeze or some other cented spray in it. And see if the odor spreads through the house.
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Old 09-11-2009, 09:15 AM   #15
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Bad smell from central air unit


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Originally Posted by beenthere View Post
Spray Febreeze or some other cented spray in it. And see if the odor spreads through the house.
I like this idea. Make sure whatever it is has a strong scent.

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