1978 Ford FiestaFACTORY OEM SERVICE PROCEDURE

Thermostatic Air Cleaner: Testing

  1. Ensure ambient temperature is above 60°F (16°C). If vehicle is equipped with cold weather modulator, by-pass the modulator by disconnecting hoses from modulator and using a suitable tube to connect them together.
  2. Apply parking brake and block drive wheels. Remove air cleaner cover. Visually inspect all components for damage. Remove parts necessary to see into snorkel and view the door.
  3. With engine off (no vacuum), door should be in the heat off position (down). If not, check door for binding or sticking. Place a thermometer as near to the bimetal sensor as possible and start engine.
  4. If door is open, turn off engine. Cool temperature sensor and restart engine. Observe door. It should now be closed. If so, go to next step. If it is still open, check vacuum components for malfunction.
  5. If door is closed, reinstall air cleaner cover (without retaining nuts). With engine running, observe air door and record the time. Door should open within five minutes.
  6. If not, remove cover and note temperature. If temperature is more than 75°F (24°C), replace the bimetal sensor. If temperature is less than 75°F (24°C), reinstall cover and run engine an additional 5 minutes. Check door position. If door is not open, replace sensor.
  7. Turn off engine. Remove thermometer from air cleaner. Reinstall all components. As a final test, apply external vacuum of 16" Hg to the vacuum motor and hold this level. Motor should remain closed for at least one minute. In not, replace duct and valve assembly.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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