Smelling units

we keep getting called to a schools IT department where they complain of the units smelling. There are probably 8 or 9 split units in total, each in different classrooms.
The problem is with only a select few where the teacher keeps complaing " there is a smell coming from the AC"

The units are about 12 months old and like new. Each time we get on site, we spray coil cleaner on the indoor coils, rinse through the coils and the tray with water and then put a smelly jelly in the return air on top of the filter.

This works for a few weeks but then we get the call again saying they are smelling.
What causes some units to smell and not others. Is it stagnant water in the tray? Or is it something else?

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Originally Posted by marc5180

we keep getting called to a schools IT department where they complain of the units smelling.
What causes some units to smell and not others. Is it stagnant water in the tray? Or is it something else?

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Two things come to mind when I read your post.

Firstly sometimes the evap does smell when it goes from cooling to heating for a short while as it evaporates the moisture on the coil. Its not an unpleasant smell just distinctive.

Secondley I would look to the teacher or class.
Some people actualy do not belive in air cond and think that they are the creator of a lot of problems we have (such as sick building syndrome and such like). I'd be tempted to do the placebo test on them.
Next time they complain go in and assure them that you have refreshed the unit without actualy doing anything.
If they are happy at that then perhaps the problem is not the machine but the person claiming to smell the smell.

taz.

Is there any kind of description as to what the smell resembles? Sometimes locker rooms effect smells. Sometimes moisture left in the ducts can contribute. Is there a drain that is not normally used meaning all of the moisture has left the traps allowing sewer gas to emit from them.

Agree with all of the above.

As you state that the units are clean, what does the condensate drain run to?

We had it on a couple of occations where the condensate has been connected to a drain of some sort via a "normal" trap, when the trap goes dry, the unit sucs air from the drains and this smells. As a result we now use HEPWORTH traps with membranes in them.

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Originally Posted by taz24

Some people actualy do not belive in air cond and think that they are the creator of a lot of problems we have
.

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My first thought was this when i went into the room and couldnt smell anything. I think i should try the test next time i get called and see if it is the person claiming to smell the smell.

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Originally Posted by BigJon3475

Is there any kind of description as to what the smell resembles? Sometimes locker rooms effect smells. Sometimes moisture left in the ducts can contribute. Is there a drain that is not normally used meaning all of the moisture has left the traps allowing sewer gas to emit from them.

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The teachers seem to think its a musky smell, when i walk into each room i genuinely can't smell anything.

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Originally Posted by The Viking

Agree with all of the above.

As you state that the units are clean, what does the condensate drain run to?

We had it on a couple of occations where the condensate has been connected to a drain of some sort via a "normal" trap, when the trap goes dry, the unit sucs air from the drains and this smells. As a result we now use HEPWORTH traps with membranes in them.

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Each of the cassettes have seperate drains with a trap on that all tee off 1"1/8 drain that runs the length of the building (about 25-30m) then into a main soil stack

I would be looking at moisture left over in ducts if your getting a musty smell. If all moisture is not removed from ducts after colling shuts off. It has a chance to sit in the duct work, drain pan, and trap. It probably resembles the musky smell when you cut your car off while it's a/c is running and then when you get back in and run the a/c at first you get a real musky high RH situation. Possible fixes would be run a delay off timer to help dry out the duct work. After cooling process is done with an evap. coil the air leaving the evap. is close to 90-95% relative humidity. When the system shuts off all that moisture is still left there to absorb into insulation and what not. I'm a residential guy so not formiluar with your situation just throwing ideas out.

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Originally Posted by marc5180

Each of the cassettes have seperate drains with a trap on that all tee off 1"1/8 drain that runs the length of the building (about 25-30m) then into a main soil stack

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So, if the trap for an individual unit dries out, then that unit would suck air from the main soil stack?
:rolleyes:


:cool:

Hello All,

From my experience there are two types of smell that can come from a fan coil unit.

The first is from bacteria on the heat exchangers. The smell occurs when the bacteria goes from a wet state to a dry state or vice versa. A good strong disinfectant can clear this up but you can always get the bacteria back on the coil. The bacteria comes from dirty carpets, curtains, and people (smelly armpit and all that). It can also come from beauty products like make up and perfume. (Though you would be very brave to tell a woman she is wearing cheep perfume)

The second smell can occur if the oil used during the manufacture of the coil was not dried fully. Once the coil is made and the copper tube is compressed into the fins the entire coil is baked in the oven to completely evaporate the oil. If this process was not carried out correctly when the unit is operated in heating you will get a very strong smell. To get rid of this you need to spray the coil with a good degreaser and then run the unit in maximum heating for 24 hours.

Marc5180 looks like you have your work cut out at the school with all those smelly teenagers :eek:

Regards

Obi Wan

When i took off the cover at the side of the unit to get access to the tray ( where you put in water near the lift pump) there was a positive pressure so would it not be the same 2 inches above at the outlet of thedrain? If so then how would the smells get back to the unit?

If you do a search for "dirty sock smell" in google you will find a good bit of info on this subject. Coil manufacturers have been dealing with this recently and for now the only solution seams to be a coil with an epoxy or electro-coating on it to resist the growth of bateria on the coil.
It seams to happen when new units are put in place with existing ductwork. I guess the ductwork harbers the bateria and promote the growth on the coils.
UV Lighting before and after the coils could be another option, but I'm not sure if there is any data to back this up.

Have had several smelly units that were installed sightly off level and water was forming in the drain pan on the opposite side to the outlet.

Result was the remaining water in the pan would go stagnant and would smell very bad at startup.

This condition was aggravated when you would switch to heating after long periods of cooling.

If you get hold of the unit and physically pull it to tilt towards the drain outlet side it can sometimes cure this problem.

Thats a good point Temprite thanks, i'l have a look next time i get called back to site which i'm sure will be very soon.
Marc

hi friend! let me ask you,in these splits did you pyt the inside drain in to the outer unit? this causes bad smells from the standing water in to the outer unit.

similar problem with similar IT geeks, resolve was fresh air make-up and issuing soap and insisting on daily showering by students. Geeks don't shower daily as they are constently cruising the NET and nothing else matters. Festering armpits and others areas.
magoo