Ported Vacuum Switches (PUS) are used to switch vacuum signals with varying engine coolant temperatures. They may have two, three or four vacuum ports and, on models equipped with catalytic converters and Thermactor systems, a set of electrical contacts. There may be as many as three or four separate ported vacuum switches, each with its own special function. PVS switches may be used to cut off exhaust gas recirculation until a predetermined engine temperature is reached, to switch vacuum signals on an ignition spark control system in order to improve cold start driveability, or to provide extra ignition advance and subsequent higher idle speed should the engine begin to overheat. They may also be used to vent Thermactor pump air to the atmosphere under certain engine conditions, or to regulate a vacuum-operated heat control in the exhaust manifold.
- Attach a tachometer and start the engine.
- Observe the reading on the tachometer.
- Disconnect the hose from the intake manifold to the control valve and plug it with a golf tee or pencil.
- Again observe the reading on the tachometer. If it has not changed, the control valve does not have an internal vacuum leak. If it does change, replace the valve.
- Reconnect the intake manifold hose to the vacuum valve.
- Block the front of the radiator with cardboard and have a friend watch the warning light on the instrument panel.
- As soon as the red warning light comes on, again observe the reading on the tachometer. It should be at least 100 rpm higher than the reading obtained in step two. If it is not, replace the vacuum control valve.
- Remove the cardboard from in front of the radiator and allow the engine to cool off before stopping the engine.
REMOVAL & INSTALLATION
- Drain about one gallon (1 gal) of coolant out of the radiator.
- Tag the vacuum hoses that attach to the control valve and disconnect them.
- Unscrew and remove the control valve.
- Install the new control valve.
- Connect the vacuum hoses.
- Fill the cooling system.