Thermostatic Air Cleaner (Tac) (Carburetor And Tbi-Equipped Vehicles; Bi-Metal Temperature Sensor; Component Replacement; Cross-Section Diagram Of The Thermostatic Air Cleaner (Tac) - Jeep cherokee 1989 Owner's Manual

6-10
4 Thermostatic Air Cleaner (TAC) (carburetor
and TBI-equipped vehicles
Refer to ihstrations 4. 1 and 4.24
General description
The Thermostatic Air Cleaner (TAC) (see illustration) provides
1
heated intake air during warmup, then maintains the inlet air
temperature within a 70°F t o 105OF operating range by mixing warm
and cool air. This allows leaner fuellair mixture settings for the car-
buretor, which reduces emissions and improves driveability.
2 Two fresh air inlets one warm and one cold
-
balance between the t w o is controlled by intake manifold vacuum. A
vacuum motor, which operates a heat duct valve in the air cleaner,
is actuated by intake vacuum.
3
When the underhood temperature is cold, warm air radiating off
the exhaust manifold is routed by a shroud which fits over the manifold
up through a hot air inlet tube and into the air cleaner. This provides
warm air for the carburetor or throttle body, resulting in better drive-
ability and faster warmup. As the temperature inside the air cleaner
rises, the heat duct valve is gradually closed by the vacuum motor
(which, in turn is controlled by a bi-metal temperature sensor inside
the air cleaner) and the air cleaner draws air through a cold air duct
instead. The result is a consistent intake air temperature. A time delay
valve provides approximately 100 seconds delay before allowing the
heat duct valve to completely close.
4 On some models, a trap door system opens in a similar manner
to close off the air cleaner from the outside air when the engine is
inoperative.
Checking
General operation
Note: Make sure the engine is cold before beginning this test.
Always check the vacuum source and the integrity of all vacuum
5
hoses between the source and the vacuum motor before beginning
the following test. Do not proceed until they're okay.
6 Apply the parking brake and block the wheels.
7
Detach the flexible duct (if equipped) from the air cleaner snorkel
(see Chapter 4).
8 With the engine off, observe the heat duct valve inside the air
cleaner snorkel. It should be fully open (heat off position). If it isn't,
it might be binding or sticking. Make sure it's not rusted in an open
or closed position by attempting to move
can usually be freed by cleaning and oiling the hinge. If it fails to work
properly after servicing, replace
9 Start the engine. Note the position of the heat duct valve. Now
it should be fully closed to incoming air (heat on position).
4.1 Cross-section diagram of the Thermostatic Air Cleaner (TAC) assembly used on carburetor and TBI-equipped
1 Heat duct valve
vacuum motor
2 Trap door vacuum motor
(not on all models)
The Motor Manual Guy
Chapter 6 Emissions and engine control systems
-
are used. The
it by hand. If it's rusted,
it.
-
models shown in open (heat off) position
3 Trap door time delay valve
(not on all models)
4 Vacuum source

Bi-metal temperature sensor

1 0 Have an assistant rapidly depress and release the accelerator 112
to 314 of its travel. The heat duct valve should briefly remain stationary,
move toward the heat off position, then back to the heat on position.
11 Loosely attach the flexible duct to the air cleaner and warm the
engine t o normal operating temperature. Remove the flexible duct and
observe the heat duct valve. It should be either fully open or at a mixture
position (half open) that provides the correct temperature for the inlet
air to the carburetor or throttle body.
1 2 Stop the engine and connect the flexible duct t o the air cleaner.
13 If the air valve does not function as described above, look for a
mechanical bind in the linkage and disconnected vacuum hoses or air
leaks at the vacuum motor, bi-metal sensor, time delay valve, check
valve, intake manfold or vacuum hoses.
1 4 If the heat duct valve manually operates freely and you cannot find
any hose disconnections or leaks, attach a hose from an intake manifold
vacuum source directly to the vacuum motor and start the engine.
a) If the heat duct valve closes, either the thermal switch, time delay
valve or check valve is defective.
b) If the heat duct valve does not close, replace the vacuum motor.
Bi-metal temperature sensor
15 Detach the t w o vacuum hoses from the sensor.
1 6 If necessary, remove the sensor (see the replacement procedure
below) and cool it below 40°F in a freezer.
17 Attach a vacuum pump to one of the sensor's vacuum fittings and
a vacuum gauge to the other fitting.
1 8 Apply 1 4 in-Hg vacuum to the sensor.
1 9 With the switch at a temperature below 40°F, the gauge should
indicate a vacuum. Disconnect the vacuum pump momentarily to relieve
the vacuum.
2 0 Warm the switch above 55OF and again attempt to apply vacuum.
There should not be steady vacuum reading on the gauge.
21 Replace the sensor if it's defective.

Component replacement

Heat duct valve vacuum motor
2 2 Remove the air cleaner (see Chapter 4).
23 Clearly label, then detach the vacuum hoses from the heat duct
valve vacuum motor, bi-metal sensor and trap door vacuum motor (if
equipped).
2 4 Drill out the rivet which secures the heat duct valve vacuum motor
to the snorkel (see illustration).
25 Lift the motor and tilt it to one side to detach the motor linkage
from the heat duct valve assembly. Remove the motor.
it
26 Installation is the reverse of removal. If you don't have a rivet tool,
you'll need a self-tapping sheet metal screw of the correct diameter
t o attach the vacuum motor t o the snorkel. Make sure the rivet (or
the screw) does not interfere with the movement of the heat duct valve.
6 Check valve
7 Time delay valve
8 Heat duct valve
9 Heat duct
10 Cool air inlet