Tac System Operation; Tac System Testing; Thermal Sensor Operation - Jeep 1979 CJ-5 Technical & Service Manual

FUEL SYSTEMS
For 1979, all Jeep vehicles are equipped with a vac-
uum-operated TAC system.
This system consists of a heat shroud at the exhaust
manifold, a hot air hose, a special air cleaner assembly
equipped with a thermal sensor, and a vacuum motor
and air valve assembly (fig. 1J-80). The air cleaner snor-
kel is attached by flexible hose to the ambient air inlet at
the front of the engine compartment.
AIR BLEED T H E R M A L
V A L V E (OPEN) SENSOR
SNORKEL A I R V A L V E CLOSED
( H E A T OFF POSITION)
A I R V A L V E OPEN H E A T E D
( H E A T ON POSITION) A I R
Fig. 1J-80 TAC System—Typical
OPERATION
The position of the heat valve is controlled by mani-
fold vacuum acting against a spring. Manifold vacuum is
controlled by a temperature-sensitive switch in the air
cleaner housing.
During engine warm-up, the temperature-sensitive
switch applies vacuum to the TAC vacuum motor. The
valve is held in the heat On position. Exhaust manifold-
heated air flows to the air cleaner. As the temperature
of the incoming air approaches 90°F (32°C), the temper-
ature switch vents vacuum to atmosphere, allowing
spring pressure to push the valve to the heat Off posi-
tion. Air flows from outside the vehicle, through the
ambient air duct, to the air cleaner.
During hard acceleration, manifold vacuum drops.
This causes the TAC valve to move to the heat Off
position, regardless of temperature, providing max-
imum airflow.
TESTING
(1) Remove air cleaner assembly from engine and
allow to cool to room temperature.
(2) After cooling, sight through air cleaner snorkel
to observe position of air valve. It should be fully open to
outside air (heat Off position)..
(3) Install air cleaner assembly to engine and con-
nect hot air tube and manifold vacuum hose.
(4) Start engine and observe position of air valve. It
should be fully closed to outside air (heat On position).
(5) Move the throttle lever rapidly to approximately
1/2 to 3/4 opening and release. Air valve should open
and then close again.
(6) Allow engine to warm to operating temperature
and observe position of air valve. It should be fully open
to outside air (heat Off position).
If air valve does not move to heat On position at
temperature below 83°F (28°C) with vacuum applied,
check for a mechanical bind in the snorkel, disconnected
vacuum motor linkage or vacuum leaks in hoses or con-
nections at the vacuum motor, thermal sensor and in-
take manifold.
If air valve mechanism is operating freely and no
vacuum leaks are detected, connect a hose from an in-
take manifold vacuum source directly to vacuum motor.
If air valve now moves to heat On position, replace
thermal sensor.
If air valve remains in heat Off position, replace air
cleaner body and vacuum motor assembly.
THERMAL SENSOR
i i p i i c i f f l i i f
(1) Remove air cleaner and disconnect vacuum
hoses from sensor.
(2) Break vacuum nipples off sensor. Remove sen-
sor and gasket from air cleaner.
(3) Install replacement sensor and gasket. Press re-
tainers over vacuum nipples.
(4) Connect vacuum hoses and install air cleaner.