1991 Acura Legend Base, AutomaticFACTORY OEM SERVICE PROCEDURE

Air Conditioning Signal

  1. Connect PGM-FI test harness between the ECU and ECU connectors. Disconnect connector "C" from main harness only; DO NOT  disconnect from ECU. Turn ignition on.
  2. Measure voltage between ECU terminals C3 (positive) and A26 (negative). If voltage is not about 10 volts, substitute a known good ECU, and recheck voltage.
  3. If voltage is about 10 volts, reconnect connector "C" to main wiring harness. Touch terminals A15 to A26 together and check for clicking of A/C clutch.
  4. If A/C clutch clicks, go to next step. If A/C clutch does not click, jumper Red/Blue wire of A/C clutch connector to ground. If A/C clutch clicks, repair open in Red/Blue wire. If A/C clutch still does not click, repair A/C clutch circuit.
  5. Start engine, and turn blower on. Turn A/C switch on. If A/C operates, A/C signal is okay. If A/C does not operate, measure voltage between terminals C3 (positive) and A26 (negative).
  6. If voltage is more than 1 volt, repair open in Blue/Black wire between C3 and cooling fan control unit. If voltage is less than 1 volt, substitute a known good ECU, and recheck voltage.
Factory Service Tools

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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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