AHU controllers were used extensively for controlling air handling units, especially for complex units requiring more I/O interfaces than the UNT. Many FEC controller models can replace an AHU controller, but the FAC3613 is an ideal replacement because it has an equivalent number of onboard I/O. You can also use a CGM09090 to replace an AHU controller. If the FAC3613 or CGM09090 controller does not have enough onboard I/O to meet the replacement application requirements, then add IOM or XPM series Expansion I/O Modules.