Evaporator freeze-up

I have a Coleman Mach 15, Model 48204-669 that the evaporator starts to freeze up after about 45 minutes of running, reagrdkess if outside temperature. The unit does have an A/C connect by KoolRV installed on the ducted system since 2024. The "freeze-up" problem has become worse in the past couple of weeks. I noticed yesterday that I could not hear a distinct change in fan motor speed when switching the unit from low to hi speed at the thermostat Does anyone have any information on this particular units fan motor as to whether ituses a resistor or solid state relay to change the speed of the motor? Thanks for any assistance