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HOMESERVICE MANUALSMERCURY1991TRACER BASE, 4D SEDAN, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 143 (HVAC SYSTEM - A/C-HEATER SYSTEM - AUTOMATIC)TESTINGEATC SYSTEM TEST
1991 Mercury Tracer Base, 4D Sedan, Automatic

EATC System Test

1991 Mercury Tracer Base, 4D Sedan, AutomaticSECTION EATC System Test
WARNING: This page is about a different car, the 1996 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: Before performing this test, perform system self-diagnostics. See SELF-DIAGNOSTIC TEST.

  1. Check Blower Manual Override Low Speed

    Operate A/C system in AUTOMATIC mode. Rotate blower motor thumbwheel to lowest speed position. If blower motor runs at low speed, go to next step. If blower motor does not run at low speed, go to TEST "D".

  2. Check Blower Manual Override High Speed

    Rotate blower motor thumbwheel to highest speed position. If blower motor runs at high speed, go to next step. If blower motor does not run at high speed, go to TEST "E".

  3. Check Defrost Manual Override Operation

    Press DEF (defrost) button. Most air should flow from defroster nozzles, with a small amount flowing from side demisters. Outside/recirculated air door should be in outside (fresh) air position. If system operates as specified, go to next step. If system does not operate as specified, go to VACUUM SYSTEM TEST.

  4. Check FLOOR Manual Override Operation

    Press FLOOR button. If air flows from floor ducts, go to next step. If air does not come out of floor ducts, go to VACUUM SYSTEM TEST.

  5. Check VENT Manual Override Operation

    Press VENT button. If air comes out of panel vents, go to next step. If air does not come out of panel vents, go to VACUUM SYSTEM TEST.

  6. Check MAX A/C Manual Override Operation

    Ensure ambient temperature is greater than 40°F (4°C). Press MAX A/C button. If outside/recirculated air door is in recirculated air position, go to next step. If door is not in recirculated air position, go to VACUUM SYSTEM TEST.

  7. Check Clutch Engagement In VENT Mode

    Press VENT button. VENT should be displayed on the Vacuum Fluorescent Display (VFD) window and the compressor clutch should be off. If system operates as described, go to next step. If system does not operate as described, check A/C clutch.

  8. Check MAX A/C Mode Operation

    Press MAX A/C button again. MAX A/C should be displayed in VFD window, and compressor clutch should engage. If system operates as described, go to next step. If system does not operate as described, check A/C clutch.

  9. Check AUTOMATIC Mode

    Press AUTOMATIC button. The selected temperature and AUTOMATIC should be displayed in VFD window. If system operates as described, system is operating correctly at this time. If system does not operate as described, go to SYMPTOM DIAGNOSIS under TROUBLE SHOOTING.
RENDER: 1.0x

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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.