i have three York Affinity units with variable fan speeds. model number is AVY24B3XH21A-they are about 5 years old, the same age as the house. Its a new house, all new duct etc. One of them has a nice high fan speed and cools the rooms nicely. the other two have very low fan speeds that I cannot raise. the dip switches on each of the fan cabinet circuit boards are identical, and the thermostats are identical, and all wired the same. Venstar T1800.