Dirt floor crawlspaces are, by definition, sources of mold. Molds live in the soil, and once the soil is enclosed by foundation walls but left exposed beneath your home, or a section of your home, there will be (or already is) a mold problem to contend with.
In areas where full basements could not be dug or to save money when building an addition, builders often left exposed ledge, boulders, and dirt. A lot of dirt. Sometimes the dirt is only a couple of feet beneath your floors, other times it can be six feet below. The closer the dirt is to your living space, the higher the risk that you will see and/or smell a mold problem in the house. Dampness in the dirt will migrate up into your floors, causing cupped hardwood floors or musty smelling carpets. Mold spores in the dirt will naturally become airborne and land on damp wood surfaces, like the underside of your family room floor, for example. If there is enough moisture for the mold spores to germinate and grow on the flooring, you will likely smell a musty odor or notice an overall damp feeling in the family room.
Solutions to dirt floor crawlspaces can include sealing the dirt permanently with a layer of concrete or a less permanent plastic layer, both installed professionally. An exposed dirt floor crawlspace cannot be ‘dried out’ with ventilation or dehumidification. There is simply too much surface area and continual moisture coming out of the soil for either of those to work. Using a dehumidifier in a dirt floor crawlspace is not only a drain on your electric bill but it will also stir up mold on the surface of the dirt and make the spores go airborne: something that you definitely don’t want.
By sealing the crawlspace dirt, you remove most of the moisture source. The crawlspace will still need to be dehumidified to maintain low relative humidity. And, you still have the mold. Removing the moisture does not remove the mold. Depending on the severity of the mold problem (which is where your consultant like Gordon Mycology can help), you may need to bring in a specialized mold remediation company.