A three part valve is provided. The valve has a housing having three axially spaced inlet ports and an outlet port. A rotary valve assembly with a modular rotor is provided for controlling fluid communication between the inlet ports and the outlet port. The rotary valve assembly includes a shaft. Additionally there is provided a first generally cylindrical valve module torsionally affixed with the shaft for controlling fluid communication between a first inlet port and the outlet port. The rotary valve assembly also includes a second generally cylindrical valve assembly rotatably mounted on the shaft controlling fluid communication between a second inlet port and the outlet port. The second valve module has a coupling interface with the first valve module. A third generally cylindrical valve module is also provided rotatably mounted on the shaft. The third cylindrical valve module controls fluid communication between a third inlet port and the outlet port. The third valve module has a coupling interface with the second valve module.