Vacuum Control Valve

The VCV controls vacuum to other emission devices during engine warm.up: the 2-port types simply open when engine coolant reaches their pre-determined calibration temperatures; the 4-port types open likewise, since they are nothing more than two 2-port types in one housing; and the 3-port types switch the vacuum source to the center port from the top or the bottom ports. Electrical switches can be either open or closed until the VCV is fully cycled. Most VCV's respond to a sensing bulb immersed in engine coolant by utilizing a wax pellet principle. The only exception is the 9F454 which operates on a bimetal principle. Vacuum is usually sourced as illustrated in Figure 1.











Electrical Vacuum Switch

The electrical vacuum switch (Figure 2) could be either opened or closed at room temperature. It will be reversed (opened to closed or closed to opened) with the engine at full operating temperature.