A variable cam timing phaser including a housing, a rotor coaxially
located within the housing, a phase control valve, a switching valve, and
a passage connecting the first advance and retard chambers. The housing
and the rotor define at least two chambers, a first chamber separated by
a first vane into the first advance and retard chambers, and a second
chamber separated by a second vane into the second advance and retard
chambers. The switching valve has a first position in which fluid may
flow freely between the passage connecting the first advance and retard
chambers and fluid flow from the phase control valve to the first advance
and first retard chambers is blocked. In the second position, the passage
connecting the first advance and retard chambers is blocked and fluid may
flow freely between the phase control valve and the first advance and
first retard chambers.