On 11 April 2014 15:22, veegee wrote: *I recently moved into a new place which came with a relatively modernwindow AC unit. When the unit is fully on (fan + compressor), that is, when it's actively cooling the air, everything seems to be working normally.However, when the compressor turns off to keep the temperature at the set* *value, there's an extremely foul smell expelled from the unit.* ____________ Something very similar happened to me a few weeks ago, but the problem turned out to be a large dairy farm of about 200 Buffalo permanently resident in open sided sheds right next to my hotel. I found that using the large ceiling fan was a workaround - but that after a day or so one became accustomed to the smell and hardly if at all noticed it. YMMV :-) In your case, it's possible that the system has an internal mould growth. Thi happens in car air-conditioning systems and the smell can be "annoying" at best. I could make up relatively plausible but not necessarily correct theories to explain the do/don't smell it aspects in your case, but Occam suggests that it's easy to dry disinfection of your system. I understand that you can buy products for spraying into car systems for this purpose. If I was doing this I'd consider a suitably dilute aerosol spray of chlorine bleach (usually sodium hypochlorite) with a suitable means [tm] of preventing the outflow from bleaching your room and contents. I'd guess that 0.1% or maybe even lower would be a suitable starting point. the possible corrosive effect on the system needs to be considered. Probably very OK but tbd. Another possibility is "BAQ" (aka Benzyl Alkonium Chloride aka Quaternary Ammonium Salts aka ... many similar names) which, as you may be aware, is the primary disinfectant material on the residential market these many many decades (at least 4). You can but it in very very expensive forms but usually chain stores have their own brand at around 2% concentration at far lower cost per litre-% than most alternatives. Again, use at about 0.1% probably OK. When used very strong and aerosoled it can have a nasty effect on breathing (ask me how I know) but at concentrations of <=3D 0.01% can apparently be used as gargle, eye wash, hand sanitiser and more. I'd guess that 0.1% would be relatively benign. When STUPIDLY drunk as residue from a cup tht it NEVER should have been in at was 50% but diluted so what you get is ???% and probably 1-10% range it persuades you to pick up the bottle and go to the local 'emergency room'. A few hours of unpleasantness but no obvious long term effects. (Ask me how I know). Unlikely to hurt AC system. Russell --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .