Nissan Pick-ups and Pathfinder 1970-1988

Automatic Temperature Controlled (ATC) Air Cleaner

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OPERATION



See Figures 1, 2, 3, 4, 5, 6 and 7

The rate of fuel atomization varies with the temperature of the air with which the fuel is being mixed. The air/fuel ratio cannot be held constant for efficient fuel combustion with a wide range of air temperatures. Cold air being drawn into the engine causes a denser and richer air/fuel mixture, inefficient fuel atomization, and thus, more hydrocarbons in the exhaust gas. Hot air being drawn into the engine causes a leaner air/fuel mixture, for efficient atomization and combustion which decreases in the exhaust gases.

The automatic temperature controlled air cleaner is designed so that the temperature of the ambient air being drawn into the engine is automatically controlled, to hold the temperature of the air and ,consequently, the fuel/air ratio at a constant rate for efficient fuel combustion.

A temperature sensing vacuum switch controls vacuum applied to a vacuum motor operating a valve in the intake snorkel of the air cleaner. When the engine is cold or the air being drawn into the engine is cold, the vacuum motor opens the valve, allowing air heated by the exhaust manifold to be drawn into the engine. As the engine warms up, the temperature sensing unit shuts off the vacuum applied to the motor which allows the valve to close, shutting off the heated air and allowing cooler, outside (underhood) air to be drawn into the engine.



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Fig. Fig. 1: Automatic temperature control air cleaner-1985-86 Z20 and Z24 engines (USA)



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Fig. Fig. 2: Automatic temperature control air cleaner-1986-88 Z24i engines



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Fig. Fig. 3: Automatic temperature control air cleaner-1977-80 (Calif. and Canada)



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Fig. Fig. 4: Automatic temperature control air cleaner-1977-80 (49 State)



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Fig. Fig. 5: Automatic temperature control air cleaner-1981-83



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Fig. Fig. 6: Automatic temperature control air cleaner-1984



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Fig. Fig. 7: Automatic temperature control air cleaner-1985-86 Z24 engines (Canada)

SERVICE



See Figures 8, 9, 10 and 11

When the air around the temperature sensor of the unit mounted inside the air cleaner housing reaches 100°F (38°C), the sensor should block the flow of vacuum to the air control valve vacuum motor. When the temperature around the temperature sensor is below 100°F (38°C), the sensor should allow vacuum to pass onto the air valve vacuum motor, thus blocking off the air cleaner snorkel to underhood (unheated) air.

When the temperature around the sensor is about 118°F (48°C), the air control valve should be completely open to underhood air.

When the engine is operating under a heavy load (wide open throttle acceleration), the air control valve fully opens to underhood air in order to obtain full power no matter what the temperature is around the temperature sensor.

If the air cleaner fails to operate correctly, check for loose or broken vacuum hoses. If the hoses are not the cause, replace the vacuum motor in the air cleaner.



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Fig. Fig. 8: Testing the vacuum control motor



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Fig. Fig. 9: Testing the temperature sensor



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Fig. Fig. 10: Air control valve-closed



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Fig. Fig. 11: Air control valve-open

 
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