System Operation - Winnebago 1987-1989 LeSharo Service Manual

EMISSION CONTROL SYSTEMS
SYSTEM OPERATION
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The thermo valve (16) is connected to the
radiator.
Below 15°C (59°F), the thermo valve is closed.
Above 15°C (59°F), the thermo valve opens the
vacuum circuit from the intake manifold to the
differential pressure switch (20) and to the
vacuum reservoir (19).
The EGR valve (22) opens or closes the passage
from the exhaust manifold to intake manifold.
The amount of exhaust gas allowed to pass is
controlled by the orifice (1) located in the exhaust
manifold.
Vacuum causes the EGR diaphragm to open the
valve.
The source of the vacuum is close to the throttle.
The vacuum is controlled by the EGR valve
solenoid (21).
The solenoid (21) has voltage applied at all times.
The differential pressure switch (20) has two
chambers (A and B) separated by a diaphragm.
There is a calibrated hole located in the
diaphragm.
One side of the diaphram is controlled by a spring.
The diaphragm either opens or closes the internal
ground circuit contact.
Above 15°C (59°F) the thermo valve (16) is open.
C7-2
Chamber B of the differential pressure switch is
connected to the intake manifold via the thermo
valve.
Chamber A of the differential pressure switch is
also connected to the intake manifold, but via the
vacuum reservoir (19).
When the engine is operating at a stabilized RPM,
the pressure is equal on both sides of the
diaphragm.
The ground circuit contact is open, the solenoid
(21) is de-energized and the EGR valve (22) is
closed.
If the throttle is opened, the vacuum in chamber B
decreases immediately.
In chamber A and in the vacuum reservoir, there is
no immediate pressure variation.
The vacuum differential between chamber A and
B causes the diaphragm to move and close the
ground circuit contact.
The solenoid (21) is then energized.
Vacuum is applied to the EGR valve diaphragm
and the exhaust gas flows to the intake manifold.
The vacuum decreases slowly in the chamber A
and in the vacuum reservoir (19).
The spring forces the diaphragm and opens the
ground circuit contact.
The solenoid (21) is de-energized and EGRvalve
(22) is closed.