Arrgh: I can't find the "Comfort Curve", but it's in my HVAC reference materials. See:
OSH Answers: Thermal Comfort for Office Work
Anyway there is this curve which uses summer/winter, temerature and RH and the % of people comfortable.
If the dehumidifier was really smart, it would use this comfort curve, temperature and RH and adjust the humidity.
If it was of average intelligence, it would control the fan based on it's humidity setpoint. It would turn on based on an indoor sensor and off based on the RH in the return duct.
Somebody is pulling your leg.
Dehumidifiers essentially make it more comfortable without excessively cooling the air hence possibly saving energy.
The best a stupid thermostat can do is run the system longer to reduce humidity, but it cannot control it.
Something is seriously wrong here. Can you post some info about the Carrier system like model #'s of unit and thermostat?