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Testing One-Way Valves
Many vacuum operated circuits use in-line one-way valves to apply vacuum in one direction only. To test the function of the valve remove it from the circuit. Attach
the VS401 vacuum tester (fig.7) and operate pump to apply vacuum. In one direction the valve should hold vacuum and in the opposite direction it should not.
Testing Electrically Operated Vacuum Solenoids
Electrically operated vacuum solenoids are commonly used in control circuits for air conditioning / ventilation systems, emission control systems, idle step up
systems etc. and testing the function of these when using the VS401 is extremely simple. Locate the solenoid to be tested and remove the line that goes to the
component being tested. Connect the VS401 to the solenoid port (fig.8) and start the engine. With the system turned off there should be a zero gauge reading.
Now turn the system to the 'on' position and a gauge reading equal to the manifold vacuum should be observed, tf no reading exists remove the vacuum
supply line and test for manifold vacuum at this point. If the vacuum does exist this indicates that the solenoid is faulty or it is not receiving a 'switch on' voltage
(use a multimeter to test this). If no vacuum exists trace the supply line back to the vacuum source checking for kinks and breaks.
Testing Thermal Vacuum Switches
There are many vacuum controlled circuits that must only operate when the engine reaches normal operating temperature. This is done using thermal switches
that remain in an 'off' position until a given temperature is reached. To test this type of switch, remove the vacuum supply line coming from the manifold to the
switch and test for manifold vacuum. If this vacuum is correct refit the supply line to the thermal switch and remove the opposing line from the switch. Attach the
VS401 vacuum tester to the port (fig.9) and start the engine. With a cold engine no reading should be noted. When the engine reaches normal operating
temperature a manifold vacuum reading should be noted.
fig.8
fig.7
fig.9
Testing Vacuum Operated Heater Taps
Climate control ventilation systems are becoming very common on newer vehicles and most of the systems use vacuum operated taps to control the heating
modes.
On the majority of makes and models, the system uses vacuum to turn the heater tap 'on'. To test these remove the supply line from the tap vacuum module and
connect the VS401 vacuum tester (fig.10). With the engine at normal operating temperature locate and feel the heater return hose. With the heater tap in the 'off'
position, this hose should be cold. Now operate the vacuum pump to open the tap. The gauge reading must hold. If the tap is in working order, the return hose will
begin to heat. If the hose does not begin to heat this indicates that the tap is faulty.
Testing Vacuum Operated Remote Central Locking Systems
Some makes and models use vacuum operated bellows mounted in each door, to centrally lock and unlock the vehicles doors. These systems use either manifold
vacuum stored in a reservoir for use when the engine is not running or an electrically driven vacuum pump which operates when the doors are locked or unlocked.
In either system, the VS401 vacuum tester is ideal for testing each individual door bellows. To do this, remove the door trims as required. Remove the vacuum
supply lines from the bellows and attach the VS401 vacuum tester (fig.11) and operate to apply vacuum to the bellows. Wait for 30 seconds, no drop on the gauge
should be noted. If the bellows are found to be in order attach the vacuum supply line to the VS401 vacuum tester and operate system to test for vacuum supply. If
the vacuum supply does not exist or is low trace back down the lines to the vacuum supply looking for kinks, restrictions or cracked lines. Repair as required and
retest.
fig.10
fig.11
VS401 - 1 - 061006
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