Air conditioning and bad smells

[redduck]

In the last few days when turning on the air conditioner, a remarkable bad smell permeates the house--kind of eye-watering--making the house smell worse than usual. Seems like maybe there's a dead critter and his dead cousins in the ducts. But, this is just a hunch.

So, before I make my predicable (and numerous) mistakes about house maintenance, what are the prudent actions for me to take in this situation?

 

[RobbieB]

You could have mold in the evaporator pan. Sometimes the drain gets plugged and the condensate builds up and stinks.

 

[imoldernu]

Looks like you might not be the first to have the problem... Check out this site to more closely define the smell, before solving the problem...

Why Does My Air Conditioning Smell? | Air Conditioning Repair in Maryland |

 

[Walt34]

You could have mold in the evaporator pan. Sometimes the drain gets plugged and the condensate builds up and stinks.

This is by far the most likely, although imoldernu's link has other possibilities.

The good news is that if you're not comfortable taking this on yourself the cost of having a technician do it is not outlandish, it should be a 10-30 minute job depending on access issues. If the initial installation has an "uphill" grade in it (a huge no-no) that will have to be corrected and could take an additional half hour or so, again depending on access and ease of realigning the drain.

 

[redduck]

I guess I hope it is just mold in the evaporator pan. However, the entire unit is only 2+ years old. Can mold occur that quickly? We had our other HVAC unit for several decades (I can't actually remember how many) and never had this problem.

 

[samclem]

I guess I hope it is just mold in the evaporator pan. However, the entire unit is only 2+ years old. Can mold occur that quickly? We had our other HVAC unit for several decades (I can't actually remember how many) and never had this problem.

Yep, it might not take long to get a lot of mold. Just as importantly, if the water can't drain in the proper way, it could cause some very expensive repairs due to damage from where it finally leaks (this depends largely on where your evaporator coil is located. A leak in the attic or upper floor could be particularly costly).
I wouldn't think smell from mold would be quite as nasty as you are describing, but it's definitely the first thing I suspect when bad smells come from an AC unit.
Another thing--almost everyone could use a water alarm to let them know if their AC evaporator drain pan has backed up. These can be had at most hardware stores for about $20, can be easily installed, and require almost no maintenance (change the batteries, if it uses them, when you change the smoke detector batteries and check the unit for proper function by dipping the sensor in water). Drain lines often clog from built-up gook/algae, and an alarm like this can prevent thousands of dollars in water/mold damage if the existing cut-out switch fails.

 

[meierlde]

Yep, it might not take long to get a lot of mold. Just as importantly, if the water can't drain in the proper way, it could cause some very expensive repairs due to damage from where it finally leaks (this depends largely on where your evaporator coil is located. A leak in the attic or upper floor could be particularly costly).
I wouldn't think smell from mold would be quite as nasty as you are describing, but it's definitely the first thing I suspect when bad smells come from an AC unit.
Another thing--almost everyone could use a water alarm to let them know if their AC evaporator drain pan has backed up. These can be had at most hardware stores for about $20, can be easily installed, and require almost no maintenance (change the batteries, if it uses them, when you change the smoke detector batteries and check the unit for proper function by dipping the sensor in water). Drain lines often clog from built-up gook/algae, and an alarm like this can prevent thousands of dollars in water/mold damage if the existing cut-out switch fails.

Actually if properly installed there should be a drip pan under the unit to catch overflows, and a float valve to shut off the unit if the pan gets water.

 

[samclem]

Actually if properly installed there should be a drip pan under the unit to catch overflows, and a float valve to shut off the unit if the pan gets water.

Agreed. But in probably 99% of cases, that float switch in the drip pan never gets tested. Having an alarm 1) provides an important backup to the float switch and 2) tells the owner that here's water in the pan (and explains why the AC stopped working >if< the float switch did its job. Lots of people just keep running the AC when the water eventually evaporates sufficiently so the float switch resets.) So, I'm fan of these water alarms (and also put them in the drip pan for the water heater and in a drip pan for the washing machine--which also warns of a broken supply hose).

 

[redduck]

I'm having a difficult time finding an air conditioning guy to come out. But, in the meantime I've discovered that the smell does not occur when the heat is on. It only occurs when the air conditioner is on. Any ideas about why that is?

 

[Sunset]

Yep, it might not take long to get a lot of mold. Just as importantly, if the water can't drain in the proper way, it could cause some very expensive repairs due to damage from where it finally leaks (this depends largely on where your evaporator coil is located. .....

This happened to me.
I found water dripping down over the circuits and motor of the furnace.
Replaced the furnace motor and angled the pan to drain properly.

 

[samclem]

I'm having a difficult time finding an air conditioning guy to come out. But, in the meantime I've discovered that the smell does not occur when the heat is on. It only occurs when the air conditioner is on. Any ideas about why that is?

Hmmm. Do you mean that you can run the AC all day (and air coming from ducts smells bad), and if you switchover and run the heat immediately afterward the air doesn't smell bad at that immediate time? That would be a mystery, since, no matter where or what is causing the smell, it would still be occurring for at least a few minutes after you changed over to heat (because the air still goes over the A/C evaporator coil, across the pan in the bottom, through the same ducts with any dead critters, etc).
Now, if you mean that a few days or more after the last time AC has been run (and the pan/any mold has had a chance to thoroughly dry out), if you run the heat you don't notice a smell, that would indicate the problem is more likely mold related, highly unlikely to be a dead critter in the ductwork.

Two thoughts:
1) Unless you've got a highly inaccessible installation or you just don't want to mess with it, it's usually not hard to detach the drain pipe and see if a bunch of mucky water drains out. The clog is most frequently in the drain pipe itself, and cutting the PVC near the unit will let the water drain out if the clog is lower than that, and give you a chance to (carefully) push some stiff wire up there and ream it out (if the clog is upstream). Bring a bucket to catch the water/muck, and have a coupling of the proper size and some solvent (aka "PVC cement") to re-join the pipe when you are done. As a backup, have a cap of the right size that you can jam over the end if the drainage is more than you'd bargained for. Also, before you cut anything, see if the air handler has "settled" or been bumped causing the drain point (under the evaporator coil) to >not< be at the lowest part of the internal drip-pan under the evaporator coil. If it's been knocked out of kilter, the drain tube won't be at the low point, water will pool in the internal drip pan and possibly spill into the ductwork, and mold will result >even< if the drain pipe is not clogged. A regular bubble level placed vertically against the sides of the ductwork/air handler will probably tell you what you need to know: is the unit plumb (if so, the drain will be at the lowest point unless it was installed incorrectly or something has come apart inside the air handler).
2) They make UV light "air purifiers" (like this one) that can be put into your duct/air handler system and will keep any mold at bay if the affected location where it grows is within line of sight of the unit. These are seldom required if adequate drainage is provided, but it can be a good belt-and-suspenders approach as the units also kill a high percentage of other mold/bacteria/viruses normally in the air as it passes by the light. They are very reliable, but the bulb (less than 40W) needs to be changed annually. If you go this route, be sure to investigate the replacement price of the bulbs and get a unit with inexpensive ones. The "guts" of the bulbs are all very similar (essentially florescent lamp without the regular phosphor coating, so they emit a lot of UV-C light), but some companies use nonstandard ones or make the bases unique so they can charge a high price for the proprietary replacement bulbs.

 

[redduck]

Hmmm. Do you mean that you can run the AC all day (and air coming from ducts smells bad), and if you switchover and run the heat immediately afterward the air doesn't smell bad at that immediate time?....

First of all, samclem, thank you for your detailed response.

Now let me try to respond to your post:

I haven't run the AC for longer than 15 at minutes at any one time because of the smell and because I keep picturing icky, harmful things coming out of the air ducts and floating around in the air. The first few days when immediately switching over to the heat from the AC, it did seem as if the odor stopped very quickly. However, that wasn't the case today (Thurs). The bad smell continued from the system after immediately switching from the AC to the heat (the heating continued to smell bad).

Regarding your two thoughts:

I think the installation is very accessible. I finally had a AC guy come out from the same company that sold us the HVAC. I was told by other AC guys from two different companies to use the original company because some of the HVAC stuff is still under warranty (but, not labor). This original company guy just kind of opened the cover of the furnace (I think it was the furnace), checked some stuff out using a mirror and a flashlight, peeked into the attic and said he couldn't figure out what the problem was. His supervisor is coming out tomorrow.

Unfortunately today, while the smell was coming out of the system (both AC and heat), the smell wasn't quite as strong. Might that be because the system wasn't turned on for a day or two? I think you mentioned that in your post, but I might have misunderstood.

I have printed out this whole thread, highlighted the salient sections and will give it (or read it to the supervisor) if he seems to be getting stumped.

And, thanks for the link about the UV light.

 

[redduck]

The AC supervisor came out this morning. To prepare for him, we turned on the heat for about 20 minutes (no smell at all). Then, after about 3-4 minutes, we turned on the AC and the smell showed up almost immediately (2-3 minutes at most). Then the supervisor showed up, we took him over to a vent, he smelled the smell as the AC was running and said the problem was with the cooling coil coating. He said that the cooling coil needed to be replaced with one that had a different coating. Unfortunately, it's going to take 2-3 weeks to get the part from the factory. He said that it was safe for us to use both the heat and AC. We will probably use the heat as needed, but only use the AC if it becomes a true necessity.

The cooling cool is under warranty; it is not certain if labor is under warranty.

 

[ERD50]

The AC supervisor came out this morning. To prepare for him, we turned on the heat for about 20 minutes (no smell at all). Then, after about 3-4 minutes, we turned on the AC and the smell showed up almost immediately (2-3 minutes at most). Then the supervisor showed up, we took him over to a vent, he smelled the smell as the AC was running and said the problem was with the cooling coil coating. He said that the cooling coil needed to be replaced with one that had a different coating. Unfortunately, it's going to take 2-3 weeks to get the part from the factory. He said that it was safe for us to use both the heat and AC. We will probably use the heat as needed, but only use the AC if it becomes a true necessity.

The cooling cool is under warranty; it is not certain if labor is under warranty.

Is this a heat pump? This article seems to target your issue directly. It's a few years old, but if I were you, I'd do some research on the current coil coatings (or ask your guy for the info if he has it). There may be better ones since this was written.

A New Solution Found for Dirty Sock Syndrome

I still don't understand why the smell wouldn't exist with both hot and cold cycles though. If it is mold/bacteria, they are in the air path regardless. Hard to imagine something getting smelly when it's cold - but I guess the A/C is creating the condensation, so the stuff is wet with AC running, dry with heat running - that must be it?

-ERD50

 

[redduck]

I can only tell you what I think he said and what showed me: There are two metal containers on top of each other. One contains the heating coils and one contains the cooling coils. He said the problem is not mold or bacteria, but that the problem is the coating on the cooling coils. Apparently, it's a common problem. He wasn't interested in opening up any part of the HVAC system--he just stayed by the vent for a minute or so and made the diagnosis.

He didn't say anything about condensation, so I don't know about that. However, what does concern me is the potential cost of the labor. After listening to the guy, I had wondered if they could just open up the cooling system and spray it with some sort of coating to take care of the problem (it didn't occur to me at the time to ask). But, then I read the link in Erd50's post about:

"The Dirty Sock Syndrome" which mainly occurs in humid climates. Luckily, Los Angeles is not particularly humid. It also discusses applying coatings, but it is an expensive process. The HVAC guy who came to the house said that the new cooling coil system will have a different coating than the one that my system now has. Apparently, it's not like a coating that comes out of a spray can or can be painted on. It's more of how the coils are designed or made. He said something about something being further apart. Sorry that I can't be clearer than this.

 

[Walt34]

The "Dirty Sock Syndrome" is a new one on me, I'd never heard of that. From the link there is a possible solution but it's kind of expensive...

In one instance, a complaining couple underwent a divorce and when one of them moved out of the home, the problem went away.

 

[samclem]

Is this a heat pump? This article seems to target your issue directly. It's a few years old, but if I were you, I'd do some research on the current coil coatings (or ask your guy for the info if he has it). There may be better ones since this was written.

A New Solution Found for Dirty Sock Syndrome

That's an interesting article, thanks. This one is from the same journal, cites some of the same info almost verbatim, but is less optimistic about the effectiveness of coil coatings and seems to recommend UV-C light as a more effective solution:
Dirty Sock Syndrome: What It Is, How to Prevent It --Applying a Solution That Works

At the risk of being repetitious, I would recommend that if you go with a UV-C unit (or units--to assure full coverage of the coils and drip pan)that you specify one that takes low-cost replacement bulbs (you may have to go online yourself to find it) --preferably ones you can replace yourself. The HVAC guys might instead prefer to sell you one with hard-to-get and expensive proprietary bulbs, and you shouldn't let that happen. The bulbs are not technically advanced--they are nothing more than regular florescent light bulbs, but without the internal white phosphor coating.
If they want to get a newly coated coil, I'd be reluctant to pay any labor for the installation--you bought an HVAC system, why wasn't the manufacturer's coil coated in the first place if that's what it needed? You already paid to have the coil installed once--it does not seem proper for them to ask for you to pay again to install one that is now right--the way it should have been to begin with.

 

[meierlde]

I had a leaking coil replaced (the part was under warranty but the labor was not) it was about $261 about 2 hours most of which was taken up by the leak checking. They have to close the valves on the outside unit, recover the refrigerant from the loop outside the outside unit, change the coil flowing nitrogen while brazing, leak check the repair. (Pump it down and see if it holds vacuum) then refill the system with refrigerant, and check everything out.

 

[redduck]

UPDATE:

The air conditioning people are coming out tomorrow to replace the cooling coil. Apparently, the cooling coils were treated with a coating that causes a bad smell. A class action law suit has been won (I'm always the last to know) and the coil will be replaced for free. The installing company (the same one I bought the HVAC from) said that the labor is also covered. It sounded like all this is under warranty (I bought the HVAC July 2013).

Since I always seem to screw things up regarding service people are there any questions I should be asking these guys? Anything I should be doing regarding this class action suit even though it appears the system in under warranty? Anything else I need to know?..................................anything?

 

[Sunset]

Thanks for the update, incredible they would coat them with some weird random stuff an not even test it.

 

[samclem]

Since I always seem to screw things up regarding service people are there any questions I should be asking these guys?

Since they installed the system and were aware of the recall, my first question to them would be "why didn't you tell me about this recall?" They knew they had installed an affected unit, but you wouldn't have been able to get it replaced if it had started stinking after the cutoff date of the class action suit (if it has one).
I don't have any other ideas about what to check for. It might be a good idea to establish a baseline for how well the unit works now and test it again after the do their work. One unscientific way: Maybe set the thermostat to get the house to about 75 degrees and leave it there for a few hours until it is stable. Then set the thermostat to 65 degrees and time how long the unit takes to cycle off. Note the outside temperature and (ideally) do this test after the sun has set (so that solar gain isn't a factor). After the replacement is done, repeat the test when the outside temperature is about the same (a few degrees difference in outside temperature won't matter much). If it takes longer to cool the house the same 10 degrees after they have done their work, that would be a red flag. Obviously, it would be ideal to do a few trials "before" and "after" to have more confidence in your results. But--it might be too late for much of this if they are coming tomorrow. I'd try to get at least one test in, for reference.

 

[samclem]

Take a look at this page for info on the advantages of using a micron gauge when purging an A/C system. Since this repair is free to you, you'd want them to use a micron gauge when doing the purge. Leaving any water or contaminants in the system will decrease the life of your AC components and the efficiency of the system. They need to leave the vacuum pump on long enough to remove everything that's in your system, and ideally they'll flush the system a few times with nitrogen before the final pump-down.

Now, I am NOT an HVAC tech and I have no idea how common/uncommon these practices are. It could be completely unheard of in actual practice for all I know. But if they are getting a some sort of fixed fee from the AC hardware company, or if they re doing it s warranty repair work out of their own pocket, they'll have every incentive to do a slapdash job in as little time as possible, as long as your equipment survives for the warranty period of the labor. Hopefully someone with real experience will be along shortly. . .

Oh--also if the repair is "free" that should mean really free--no disposal fee for the refrigerant or fee for "reprocessing" it and adding it back to your system, no charges for use of special tools, etc. They sold you a defective coil, then didn't notify you that it was defective. You should assure this work is going to be really free.

 

[Bamaman]

Let me get this straight. Your HVAC contractor has taken 7 weeks to get this minor problem settled? And what's all this about taking weeks to get an A coil evaporator?

That's totally unreasonable. We're experiencing 95 degree days, and can get service and virtually any problem handled locally in 1 day. There are HVAC wholesale supply warehouses in every medium size or large city, and they have every available a/c part in stock.

That HVAC contractor would never have any more of my business.

I'm fortunate that I do business with a father/son HVAC team, and I can get them out within 1/2 day--sometimes within an hour.

 

[redduck]

Thanks for the suggestions and advice. The A/C guys arrived at 7:00AM as scheduled. Unfortunately, they brought the wrong coil. They brought a horizontal coil, but a vertical coil was needed (or the other way around). It seems that they are waiting for the correct coil to be delivered to the house.

 

[ERD50]

Let me get this straight. Your HVAC contractor has taken 7 weeks to get this minor problem settled? And what's all this about taking weeks to get an A coil evaporator?

That's totally unreasonable. We're experiencing 95 degree days, and can get service and virtually any problem handled locally in 1 day. There are HVAC wholesale supply warehouses in every medium size or large city, and they have every available a/c part in stock.

That HVAC contractor would never have any more of my business.

I'm fortunate that I do business with a father/son HVAC team, and I can get them out within 1/2 day--sometimes within an hour.

Agreed - my installers are here now, and when I reviewed the options with the sales guy, and asked about how long it takes to get this stuff, he said anything I choose he can get in a day or two. The equipment isn't a time factor, scheduling their install team is more limiting (and that was just a week from the time I gave them the OK - and this is major, entire furnace/AC system, going from Chimney to PVC in/out, moving the compressor, humidifier and new water heater - all day job, and water heater might stretch to day 2).

-ERD50