Thermostatic air filter (THERMAC) (3.1L engine) (Chevrolet Lumina 1)

General description

1. To ensure high driving performance of the vehicle in various climatic conditions, it is equipped with an intake air heating system. With a constant temperature of the air entering the engine, it becomes possible to more accurately adjust the fuel supply system and thereby reduce the level of combustion products released into the atmosphere, as well as eliminate the possibility of icing of the throttle valve.

2. THERMAC air filter thermostat (see illustration) is driven by heated air and the vacuum created in the collector. Air can enter the filter either from the exhaust manifold area or through the air intake in front of the radiator. The operating mode of the THERMAC thermostat is set based on the readings of the temperature sensor located in the filter housing.

Examination

3. Possible reasons for interruptions in engine operation during its warm-up:

• a) The heated air tube has become disconnected.
• b) The vacuum diaphragm does not work.
• c) No vacuum is created in the manifold.
• d) The thermostat flap does not move. /
• d) The seal on the adapter between the air filter housing and the TBI unit is missing.
• e) The air filter cover seal is missing.
• g) The air filter cover has become loose.
• c) The air filter housing has become loose.

4. The reasons for the lack of engine power and slow acceleration may be:

• a) The thermostat valve flap is jammed and does not open to allow outside air to enter.
• b) The vacuum in the temperature sensor is not released.

5. Check the condition of the system and make sure all hoses and the heated air intake are connected properly. Check for pinched, clogged or worn hoses.

6. Check the presence and condition of the sealing gasket between the air filter and the injector housing or intake manifold.

7. When the air filter is installed, the thermostat valve flap must be open to outside air.

8. Start the engine. Monitor the behavior of the thermostat valve. When the engine is first started, the damper should move and block the flow of outside air. As the engine warms up, the thermostat valve should slowly open.

9. If the thermostat does not work as described above, the damper may not move when the engine reaches the desired temperature. If you experience problems with engine throttle response during warm-up, check the condition of the temperature sensor by performing the following test.



10. With the engine stopped, disconnect the hose from the vacuum diaphragm motor.

11. Apply a minimum of seven inches (18 cm) of vacuum to the vacuum diaphragm. When this vacuum is applied, the muffler flap should completely shut off the outside air. If this does not happen, check the correct operation of the drive lever mechanism.

12. Once you have created a vacuum, try to hold it in the vacuum diaphragm motor by pinching the hose. The muffler flap should remain closed. If it opens, replace the vacuum diaphragm. The most likely cause of damage to the vacuum diaphragm is likely to be a sticking linkage or corrosion of the air intake rather than damage to the diaphragm itself. Therefore, do not rush to change the diaphragm without checking these two components.

13. If the vacuum diaphragm test shows that it is in good condition, check the condition of the vacuum hoses and the reliability of their connections. If they are also OK, replace the temperature sensor.

14. Start checking when the air cleaner temperature is below 30°C. If the engine has recently been running, remove the air cleaner cover and place the thermometer as close to the sensor as possible. Allow the engine to cool until the thermometer shows 30°C for 5-10 minutes. Replace the filter cover.

15. Start the engine at idle speed. If the engine has cooled sufficiently, the thermostat valve should immediately move and shut off the outside air. When the damper starts to open after a few minutes, remove the air filter cover and measure the temperature. It should be approximately 55°C.



16. If the thermostat valve does not open at the specified temperature, the temperature sensor is faulty and should be replaced.

Replacement of elements

Vacuum diaphragm

17. Remove the air filter cover (see chapter 4, section 8).

18. Disconnect the vacuum tube (see illustration).



19. Re-drill the two spot welds with a 1/16-inch (1.6 mm) drill bit, then enlarge the holes so that the tape clamp can be removed. Be careful not to damage the air intake.

20. Bend the clamp to the side.

21. Remove the diaphragm by tilting it sideways to disengage the lever mechanism.

22. To install the new diaphragm, drill a 7/64-inch (2.8 mm) hole in the air intake so that it passes through the center of the clamp that secures the vacuum diaphragm.

23. Install the vacuum diaphragm lever mechanism onto the thermostat valve.

24. Install the diaphragm on the air intake, securing the clamp holding it with a special screw included in the engine spare parts kit. Make sure the screw does not interfere with the operation of the unit. Shorten the screw if necessary.



25. Install the air filter cover (see chapter 4, section 8). Connect the vacuum hose to the diaphragm.

Sensor

26. Remove the air filter cover (see chapter 4, section 8).

27. Note the position of the sensor (see illustration); this will help you when assembling the unit.



28. Using a suitable tool, bend back the tabs of the sensor clamp bracket (see illustration). Remove the clamp bracket together with the sensor.



29. The sensor is installed in the reverse order. Once completed, connect two vacuum lines to the sensor pipes.

[Information taken from the official website «CHEVYMAN.RU»]