Chevrolet Full Size Cars 1979-1989

Thermostatic Air Cleaner

Print



Click image to see an enlarged view

Fig. Fig. 1 Example of a THERMAC air cleaner assembly



Click image to see an enlarged view

Fig. Fig. 2 Vacuum motor operation schematic

All engines covered by this guide utilize the THERMAC system. The THERMAC or thermostatic air cleaner system is designed to warm the air entering the carburetor when underhood temperatures are low, and to maintain a controlled air temperature into the carburetor at all times. By allowing preheated air to enter the carburetor, the amount of time the choke is on can be reduced, resulting in quicker warm-up time, better fuel economy and lower emissions.

The Thermac system is composed of the air cleaner body, an air 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 in order to supply heated air to the carburetor. A movable door in the air cleaner case snorkel allows air to be drawn in from the heat stove (cold operation) or from underhood air (warm operation). The door position is controlled by the vacuum motor, which receives intake manifold vacuum as modulated by the temperature sensor.

SYSTEM CHECKS



  1. Check the vacuum hoses for leaks, kinks, breaks, or improper connections and correct any defects.
  2.  
  3. With the engine off, check the position of the damper door within the snorkel. A mirror can be used to make this job easier. The damper door should be open to admit outside air.
  4.  
  5. Using a hand vacuum pump, apply at least 7 in. Hg of vacuum to the damper diaphragm unit. The door should close. If it doesn't, check the diaphragm linkage for binding and correct hookup. With vacuum still applied and the door closed, clamp the tube to trap the vacuum. If the door doesn't remain closed, there is a leak in the diaphragm assembly.
  6.  
  7. If a vacuum pump is not available or the cleaner passed the other tests and a problem is still suspected, leave the end of the air cleaner snorkel disconnected from the air intake duct-work, then perform a cold start of the engine. The door in the snorkel should close allowing heater air from the exhaust manifold and heat stove to enter the air cleaner.
  8.  
  9. Allow the engine to come to normal operating temperature, then check and make sure the door has opened. If the door does not operate properly, make sure the vacuum lines and temperature sensor are in good condition. If the door opened with the hand-held vacuum pump, but not when the engine warmed, the temperature sensor or the lines are likely at fault.
  10.  

REMOVAL & INSTALLATION





Click image to see an enlarged view

Fig. Fig. 3 When removing and installing the air cleaner housing, pay close attention to the fragile heat stove to make sure it is not damaged

Vacuum Motor
  1. Loosen the wing nut and disconnect the hoses, then remove the air cleaner assembly from the vehicle.
  2.  
  3. Disconnect the vacuum hose from the motor.
  4.  
  5. Drill out the spot welds with a 1 / 8 in. bit, then enlarge as necessary to remove the retaining strap.
  6.  
  7. Remove the retaining strap.
  8.  
  9. Lift up the motor and cock it to one side to unhook the motor linkage at the control damper assembly. To install:
  10.  
  11. Drill a 7 / 64 in. hole in the snorkel tube at the center of the vacuum motor retaining strap.
  12.  
  13. Insert and engage the vacuum motor linkage into the control damper assembly.
  14.  
  15. Use the motor retaining strap and a sheet metal screw to secure the retaining strap and motor to the snorkel tube.
  16.  

Make sure the screw does not interfere with the operation of the damper assembly. Shorten the screw if necessary.

  1. Connect the vacuum hose to the motor.
  2.  
  3. Install the air cleaner assembly to the vehicle making sure the hoses are properly seated. Pay close attention to the brittle heat stove to make sure it is not damaged and it is fully seated on both the exhaust manifold and the snorkel.
  4.  

Temperature Sensor


Click image to see an enlarged view

Fig. Fig. 4 Disconnect the intake and breather hoses from the air cleaner assembly



Click image to see an enlarged view

Fig. Fig. 5 Disconnect the vacuum hose from the air cleaner or from the carburetor



Click image to see an enlarged view

Fig. Fig. 6 Remove the temperature sensor from the air cleaner housing

  1. Loosen the wing nut and disconnect the hoses, then remove the air cleaner assembly from the vehicle.
  2.  
  3. Disconnect the air cleaner hoses from the temperature sensor.
  4.  
  5. Pry up the tabs on the sensor retaining clip, then remove the clip and sensor from the air cleaner.
  6.  

To install:

  1. Install the sensor to the vehicle using a new retaining clip, then secure the tabs to hold the sensor in place.
  2.  
  3. Connect the air cleaner hoses to the temperature sensor.
  4.  
  5. Install the air cleaner assembly to the vehicle making sure the hoses are properly seated. Pay close attention to the brittle heat stove to make sure it is not damaged and it is fully seated on both the exhaust manifold and the snorkle.
  6.  

 
label.common.footer.alt.autozoneLogo