Abstract: A rotary disc valve includes a valve housing having an inner surface defining an opening, a first housing port, a second housing port, and a third housing port. A rotary disc valve assembly is disposed within the opening and includes a fixed disc configured to remain stationary and a rotary disc configured to rotate relative to the fixed disc. The fixed disc includes a first flow opening providing selective fluid communication between the first housing port and the second housing port and a second flow opening providing selective fluid communication between the first housing port and the third housing port. The rotary disc defines a flow passage for distributing a fluid through the first flow opening and/or the second flow opening. A co-planar arrangement is maintained between engaging faces of the fixed disc and the rotary disc to form a fluid-tight seal therebetween.