I can't rationalize the vacuum leak hypothesis... the vents fail to work with the PBCU, regardless of the engine compartment temperature but perform flawlessly when using the HHT in the activation mode.

Again the only fault code noted so far is for the instrument cluster reporting that it is not receiving a signal on the K2 line. Inspecting both the K1 and K2 lines revealed intact wires with no faults.

The PBCU has been sent to Beckmann Technologies for inspection and possible exchange for an overhauled unit.