See Figure 1
This system is designed to warm the air entering the carburetor/TBI unit when underhood temperatures are low. This allows more precise calibration of the fuel system.
The thermostatically controlled air cleaner is composed of the air cleaner body, a filter, sensor unit, vacuum diaphragm, damper door and associated hoses and connections. Heat radiating from the exhaust manifold is trapped by a heat stove and is ducted to the air cleaner to supply heated air to the fuel system. A movable door in the air cleaner snorkel allows air to be drawn in from the heat stove (cold operation) or from the underhood air (warm operation). Periods of extended idling, climbing a grade or high speed operation are followed by a considerable increase in engine compartment temperature. Excessive fuel vapors enter the intake manifold causing an over-rich mixture, resulting in a rough idle. To overcome this, some engines may be equipped with a hot idle compensator.
- Remove the air cleaner assembly and cool to below 40°F (4°C). The damper door should be closed to outside air.
- Check for the presence and condition of the air cleaner gasket.
- Reinstall the air cleaner assembly and check to make sure the heat stove tube is connected at the air cleaner snorkel and exhaust manifold.
- Start the engine and watch the damper in the air cleaner snorkel. As the air cleaner warms up, the damper door should open slowly to the outside air.
- If the damper fails to operate, check for vacuum at the port on the carburetor/TBI unit. If vacuum is not present, the port must be unclogged.
- If vacuum was OK at the port, check for vacuum at the damper. If vacuum is present and the damper fails to operate, the vacuum diaphragm must be replaced. If vacuum is not present, the sensor unit in the air cleaner is probably faulty.
REMOVAL & INSTALLATION
See Figure 2
- Remove the air cleaner.
- If the truck uses a plastic heat tube elbow, use a 1 / 8 in. bit to drill out the two rivets that secure it to the heat tube and remove the elbow.
- Using a 1 / 8 in. drill bit again, drill out the two rivets that secure the vacuum diaphragm assembly.
- Remove the blow down spring and the carrier assembly.
- Examine the spring clip on the hot air damper. Replace if necessary.
- Install a new assembly with two pop rivets. Install a new blow down spring.
- Install the heat elbow with two rivets, if equipped.
- Install the air cleaner.
- Remove the air cleaner.
- Label and disconnect the vacuum hoses leading to the sensor.
- Remove the two clips securing the sensor to the air cleaner.
- Position the sensor on the air cleaner.
- Install the clips securing the sensor.
- Connect the vacuum hoses and install the air cleaner.