Subaru ff-1/1300/1400/1600/1800/Brat 1970-1984 Repair Guide

Hot Air Control System

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The purpose of the hot air control system is to reduce HC emissions and improve engine performance during warm-up. This is accomplished by deflecting either cool outside air or warm engine-heated air into the carburetor, depending upon engine operating conditions.

On 1970-76 models a two position control valve, mounted in the air cleaner snorkel, allows either underhood air or preheated air to flow into the air cleaner. The valve is controlled by a lever marked HOT and COLD , or WINTER and SUMMER .

When the ambient temperature is below 59°F (15°C), set the lever to the HOT or WINTER position. If the temperature is above 59°F (15°C), move the lever to the COLD or SUMMER position.

On the 1977-84 system works automatically be means of a temperature sensor and vacuum motor. The temperature sensor detects the inlet air temperature and controls the flow of vacuum to the vacuum motor. Together they regulate the air control valve, mounted in the air horn. The possible combinations of inlet (underhood) air temperatures and vacuum readings, and the resulting valve operation are shown on the Operation of the Air Control Valve chart.

REMOVAL & INSTALLATION



Temperature Sensor
  1. Remove the air cleaner cover and filter.
  2.  
  3. Using pliers, flatten the clip securing the vacuum hose to the temperature sensor and remove the hose.
  4.  
  5. Now pull the same clip completely away from the sensor. Lift the sensor off the air cleaner.
  6.  


WARNING
The gasket between the sensor and air cleaner is glued to the air cleaner and should be removed. Always install a new clip when the temperature sensor is reinstalled.



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Fig. Fig. 1 The air temperature sensor is mounted to the air cleaner



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Fig. Fig. 2 Hot air control system

Vacuum Motor
  1. Detach the connected to the vacuum motor.
  2.  
  3. Remove the screws securing the vacuum motor to the air cleaner.
  4.  
  5. Disconnect the vacuum motor valve shaft from the air control valve, and remove the vacuum motor from the air cleaner.
  6.  



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Fig. Fig. 3 Unplug the hose connected to the vacuum motor



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Fig. Fig. 4 Remove the screws securing the vacuum motor to the air cleaner



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Fig. Fig. 5 Disconnect the valve shaft from the control valve, then remove the vacuum motor

TROUBLESHOOTING & INSPECTION



Air Control Valve
  1. If the car is running, turn OFF engine.
  2.  
  3. Place a mirror at the end of the air cleaner.
  4.  
  5. Inspect the position of the air control valve. The proper position is with the fresh air vent open and the hot air inlet closed.
  6.  
  7. If the position is not as described in Step 3, check the air control valve linkage for sticking.
  8.  



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Fig. Fig. 6 Inspect the position of the air control valve with a mirror



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Fig. Fig. 7 Air control valve operating conditions

Vacuum Motor
  1. Keep mirror in position and engine OFF .
  2.  
  3. Remove the vacuum hose from the vacuum motor.
  4.  
  5. Connect a separate piece of the same type of hose to the now vacant vacuum motor. Insert the other end of the new hose into your mouth and draw in a breath, creating a vacuum in the vacuum motor.
  6.  
  7. Check the position of the air control valve. The fresh air vent should be closed and the hot air inlet open.
  8.  
  9. Now, pinch the hose attached to the vacuum motor so that the vacuum is not instantly lost. The valve position described in Step 4 should be maintained for more than 30 seconds.
  10.  


WARNING
If the conditions described in Steps 4 and 5 are not observed, replace the vacuum motor.

Temperature Sensor

WARNING
Engine must be cold before starting this test.

  1. Keep the mirror in position in front of the air horn as shown in Fig. 7.
  2.  
  3. Start the engine and keep it idling.
  4.  
  5. Check the position of the air control valve immediately after starting. The fresh air vent should be closed and the hot air inlet open.
  6.  
  7. Continue to watch the air control valve as the engine warms up. The fresh air vent should gradually open.
  8.  


WARNING
If the conditions described in Steps 2 and 3 are not observed, replace the temperature sensor.

 
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