The original symptoms last summer was that all of the a/c ductwork in
my crawlspace were sweating like nuts. The insulation on all the ducts
was soaked and dripping water. The floor insulation was also soaked
and hanging down everywhere. I also was having mold start to grow on
the joists.

I already had a vapor barrier, over the usual 80-90% of the ground.

I've owned the house for about 1.5 years. About a year before I bought
it, it had a geothermal heat pump installed.

Had a french drain and sump pump installed, as well as 2 large
ventilation fans in the crawlspace vents, at the end of last summer. I
also had new vapor barrier put down. That seemed to help at the time.
But this summer, I found that the ducts were starting to sweat again.

So I sealed up all the vents, disabled the vent fans, and put in the
dehumidifiers. Now, everything is dry. But the temperature is up
under there, and of course, I'm jacking up my electric bill. In the
short term, this is probably okay, though.

Since then, I had a patio installed, and the guys installing it
discovered that the underground drain pipe for all the downspouts on
one side of the house had been screwed up when the geothermal heatpump
was installed. The pipe was completely blocked. I think this is
probably where the moisture was coming from.

I probably also need to have the insulation on all the ductwork
replaced, though I have yet to find somebody to do this. The company
that installed the geothermal heatpump has just been jerking me around
on this for a year. I am really ****ed at them. It seems like no
other companies are willing to work on it because it is a geothermal
heatpump.

BTW, what are peoples opinions about having the existing mold cleaned
off the floor joists once the moisture problems are fixed for good?
The company that installed the french drain, sump pump, and vent fans
also sprayed some sort of anti-mold stuff under there. We've never
noticed any mold problems in the house itself (and my family would
notice this, we all have bad allergies).