Even when the compressor is not running in cooling mode and just the fan is spinning it is producing a musty smell. Where could the smell be coming from and how can I clean it? This unit does not have a tank, it re-distributes the water in cooling mode.
What I have found is the drain has gotten plugged in tha back outside section, dust builds up and plugs the hole , the other thing I have found that causes portables to smell musty is when they are installed level. There is supposed to be a tilt to the back so the condensate will run to the back and drain outside. There are special cleaners for AC systems make sure to use non acid based cleaners and flush with clear water. Acid based cleaners are very hard on the cooling fins and can start corrosion that will shorten the units life. I would want to flush my unit if musty and make sure it is draining completely or the smell will come back after cleaning .
Mold can grow on the components which are persistently wet from condensed water vapor. Google your specific model and see if you can get a procedure or even a Youtube video showing cleaning.
I would not use vinegar because it would corrode metal and the odor might persist. The usual active ingredient in most mold cleaner is some form of chlorine bleach.
For cleaning a/c refrigerator coils, I have always wanted to try hydrogen peroxide 3%, or even 4% or 7.5%. I would never use any higher concentration than 7.5%. Hydrogen peroxide is odorless and doesn't leave a residue. Fact sheet on hydrogen peroxide.
TX678G 7.5% Hydrogen Peroxide There may be regulatory restrictions on the purchase of hydrogen peroxide in larger quantities and higher concentrations due to its recent history of very, very serious misuse (production of improvised explosive devices using acetone peroxide).
Hydrogen peroxide is commercially available in 37% but the oxidizing effect of higher concentrations is much, much higher, and 37% hydrogen peroxide is a very dangerous substance. Even 3% should not be gotten in or around the eyes. Use eye protection even with 3% when it is being used for cleaning and could be splashed.
I would have thought that the portable a/c units that do not collect condensate in a reservoir or drain it by a hose to the outside would spray the condensate onto the condenser coils so that it would help cool the condenser and then would get incorporated into the hot exhaust air stream where it would be expelled to the outside. So you might have to clean both coils--evaporator and condenser.