My mother had a Trane 3 ton 16 seer system installed about 2 years ago. She lives in a approximately 1000 sf house in the San Antonio, Tx. Area.
She has been having mold problems in the registers and in the register duct boxes. The duct boxes have a insulation in them and this is constantly wet and molded. The register vents are rusted.
After some research it appears to me that the system is too large for the house. The dealer that installed it says that they did the proper diagnostic to determine the size of the system and got it signed off on by Trane.
The dealer had denied any responsibility for the problem. We have checked out any and all possible causes: plumbing leaks, duct leaks, not enough insulation, etc. The dealer says that it is nothing that they have done and asked questions like: does my mother use her oven more than the usual person would, or does she take more baths or showers, and also says that she is not turning the thermostat down enough to allow the system to run long enough to dry out the air. These questions seem highly deflective and unreasonable. I think that the dealer is skirting the real issue, but I am not sure if I have any recourse. The warranty for parts and labor has expired. All that we have is a factory warranty.
In order to reduce humidity I have heard that lowering the blower speed can help. Her system air handler is a Trane GAM5A0B36. Will lower the blower speed work and if I do this will I have a problem with the system possibly freezing up because of the lack of air blowing over the coils?

Thanks in advance for any help.

Suggest making sure that the condensation drain is open and functioning properly and installing a dehumidifier.

We have checked the condensation drain. It appears to be draining properly to the outside of the house. What do you think about lowering the blower speed?

3 ton does seem high for 1000, particularly with a 16 SEER. My son just bought a 1300 square foot house in Atlanta running a 2.5/13 but it is very shaded. Consider, however, she is in a very hot area, what about shading? What temp is she running the AC, lower than 76-77 is a possible culprit. Humidity is too high, cooling too fast, reaching dew point on metal surface and not dehumidifying as it should are the apparent issues. Lowering speed would possibly help but not sure how many speeds are available and how it would impact coils.

She runs the system at around 76 possibly as cold as 75. She has very good shade on the front of the house and not much on back.
When you mentioned a dehumidifier, were you referring to a portable unit or something in line? Thanks very much for your help.

she runs the system at around 76 possibly as cold as 75. She has very good shade on the front of the house and not much on back.
When you mentioned a dehumidifier, were you referring to a portable unit or something in line? Thanks very much for your help.

A central AC dehumidifies as it works. One problem with too big a unit is it cools too fast, shuts off and doesn't run long enough to dehumidify. I live in North GA, above Atlanta and have a Samsung portable unit. Drains out 2 gallon per day and this is in addition to the AC running. Some people run them through the wall with an AC condensate running trap. I have mine on the floor and take out the drain pan every day. I am planning to set it up to drain mine into my ejector pit after I figure the appropriate plumbing.
75 is pretty low, particularly in a humid location. Try 78 and see what happens.

Lowering the fan speed would only cause the coils to freeze up as you suspected.

You need to clean the coils with an alkali coil cleaner. You have to use a pressure washer at 1500 psi (electric pressure washer). Take out the fan and clean it, too. This will take about 4 hours or so to do. It's best to remove the coils to get them cleanest, but to do that you have to pump down unit and cut the copper lines, so you need a professional, and they hate to do that much work. It's my specialty so I do it every day. There is no other way to solve your problems except a new unit.

You need to call an HVAC expert technicians to repair your HVAC system. Always keep in mind to repair your AC or Hvac repair Orlando (http://www.myorlandoac.com/orlando-ac-repair-service/) to repair it

Being, this is NOT a SALES site. This site is free, and the link you keep providing is NOT free.