Craftsman 20930 Operator's Manual page 17

THERMAL-CONTROLLED VACUUM-SWITCHING VALVES
3) If full vacuum flows through the valve when
heated, it is okay. If there is no vacuum flow or
there is vacuum flow when the coolant is cold,
replace the valve.
Follow this procedure to test the three-port
vacuum-switching valve:
1) Apply 10" Hg of vacuum with your vacuum pump
to the middle port of the valve with a vacuum
gauge at each of the other two ports.
2) Refer to the same color-coded valves and same
temperature specifications as for the two-port valve
above. If the vacuum switches at the specified
temperature, the valve is okay. If there is no
vacuum to the lower port above the specified
temperature, replace the valve.
4-PORT PVS TEST
UPPER VALVE FLOW
RESULTS:
No vacuum when warm
Vacuum when warm
LOWER VALVE FLOW
RESULTS:
Vacuum when warm
No vacuum when warm
FIGURE 14: TESTING THE FOUR-PORT PVS
Vacuum Gauge
4) When engine is
warm (coolant
above 125°F)
Upper valve okay
Replace PVS
1) Warm engine
(above 125°F)
When engine is cold,
vacuum reading
should be zero
Lower valve okay
Replace PVS
The four-port valve must be tested two times, once
at the top two ports and once at the bottom two
ports as shown in the accompanying illustration
(FIGURE 14).
1) Apply 10" Hg of vacuum with your vacuum pump
to one of the top two ports. The valve should hold
vacuum when above the specified operating
temperature.
2) If flow occurs when the valve is warm, replace it.
3) For the lower two ports, vacuum must pass
through the valve only when the engine is warm;
otherwise, replace the valve.
3) Gauge will
read zero
2) Gauge will read 10"
1) Apply 10" vacuum
(cold engine)
3) Gauge must read
source vacuum
2) Apply 10" vacuum
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