The dust could be a small crack in the heat exchanger, return ductwork coming apart, deteriorating unit cabinet, lack of preventive maintenance or any number of other conditions. The best advice anyone can give you is to have a reputable HVAC company come over and do a complete evaluation of the entire system and see what they come up with and what they recommend.

and beware of that "m" word. it can be very pricey.
moisture is usually the cause of it. and inadequate insulation is usually the cause of the moisture.
check the drain line and be sure it is clear.
beware of legionaire's disease though, put some bleach in the drain first, wash your hands when you finish, and wear rubber gloves.

as pointed out many things can contribute.
before calling an hvac company take a look around the house.
where is heating system located?
what shape are the ducts in?
are the duct connections sealed at the plenum to the supply ducts? what about where the supply boxes meet the sheetrock ceiling? are the grills themselves dirty?
any spiderwebs at moldings?
take a strong flashlight & walk carefully in the attic if this is where ducts are located.
post back with your findings.

if you do go the hvac company route, avoid saying mold.
many companies will stay away from these homes because of liability, and rightly so as it is a big concern.
also be aware that companies that do duct cleaning usually cause more problems than they solve.

best of luck

Mould is a very serious health issue. Have it looked after quickly and properly. Consider having an independent home inspector in after everything has been done to verify the quality of the work and more importantly, the quality of the air.

SR

I'll go with the two obvious- is there a correctly installed filter in the system, and is it clean? Do they get changed regularly? Has anyone had the bad idea of turning a used one over?

What about a humidifier? Is there one, and is it being overused? Have you measured the humidity in the house? There could be inadequate fresh air replacement, or a damp problem somewhere resulting in too-high humidity. Perhaps a dehumidifier would help in the short term.

Hey energy rater la, where you been hiding? Nice to see you back in here again.

Sounds to me like you probably have two causes:
1. Ductwork has many or big leaks. This causes air to move from the living space to a space outside the living space (assuming that is where the ductwork is located), and outside air to inflitrate through cracks in the house, which brings a lot of dust, esp if #2 is true.
2. Blower runs all the time during summer months. This causes water on the evaporator coil (the one inside) to re-evaporate into the air instead of draining out through the pvc drain line. This vapor is cold, and will readily recondense in the ductwork. We strongly recommend against this practice in humid climates.

Hey guys,

I got a similar issue. I live in Arlington, VA. I have a split heat pump system. In my air handler we have found some, what looks like, mold/dust around the insulation of the cylinder shaped element that drives the blower.

I have had some people come in to look at it, and these are their respective comments:
-replace the whole heat pump system (quote 6,000-7,000 for 2 ton trane/ge air split heat pump system) as clean up (removal of insulation around the "driver") of the air handler will be so expensive that it's not worthwhile. Also, as the outside unit is 15yrs old and the inside unit (air handler/furnace) is 20yrs old you might as well replace the whole thing
- someone quoted me to clean up the airhandler for $600
- had the insurance agent come over who told me that it's not even mold
- did myself a check with bleach and mold/dust did not change the dark colour

We have tenants in the house now, and have lived for some time in the house. The house is in generally good shape and there is no smell of mold in the air handler or the house.

If this is clear to anyone, any ideas what I need to do?

Hey MrHavac!
been hiding out @ a/c classes finish early May.
bad installs drove me to it, having a blast causing
havoc in class all day.

Black marks in insulation merely indicate that air has blown through the insulation; nothing more.

"been hiding out @ a/c classes finish early May.
bad installs drove me to it, having a blast causing
havoc in class all day."
branching out huh? Good for you. The people who come here will certainly benefit from your input. Stay out of those deep south hot attics though.

The sky is falling!
The sky is falling!

There are ony a few types of mold that produce anything approaching a real hazard, and most of that may be imaginary.
Just because something smeall bad does not make it a significant hazard (nor does it mean it is not a hazard).

Arlingont, VA is pretty far out of the 'hazerdous mold' zone.

How did we ever survive for millions of years with these horrible toxic molds all areound us?

Just a couple of common problems ...

over sized AC (high humidity)
under sized ducts (high velocity water blow off)
negitive pressure in the home (dust from uncontrolled infiltration)
leaky return air ducts (pulling in dirty air)