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A/C Signal Circuit Troubleshooting

  1. Turn the ignition switch OFF.
  2. Disconnect the A/C pressure switch connector.
  3. Turn the ignition switch ON (II).
  4. Measure voltage between ECM connector terminals A27 and B20.
    Fig 1: Measuring Voltage Between ECM Connector Terminals A27 And B20
    G03692734Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there about 5 V? 

    1. YES -  Go to step 5.
    2. NO -  Go to step  12.
  5. Turn the ignition switch OFF.
  6. Reconnect the A/C pressure switch connector.
  7. Turn the ignition switch ON (II).
  8. Momentarily connect ECM connector terminals A17 and B20 with a jumper wire several times.
    Fig 2: Connecting A/C Pressure Switch Connector
    G03692735Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there a clicking noise from the A/C compressor clutch? 

    1. YES -  Go to step 9.
    2. NO -  Go to step  15.
  9. Start the engine.
  10. Turn the blower switch ON.
  11. Turn the A/C switch ON.

    Does the A/C operate? 

    1. YES -  The air conditioning signal is OK.
    2. NO -  Go to step  16.
  12. Turn the ignition switch OFF.
  13. Disconnect ECM connector A (32P).
  14. Check for continuity between body ground and ECM connector terminal A27.
    Fig 3: Checking Continuity Between Body Ground And ECM Connector Terminal A27
    G03692736Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there continuity? 

    1. YES -  Repair short in the wire between the ECM (A27) and the A/C pressure switch.
    2. NO -  Substitute a known-good ECM (see HOW TO SUBSTITUTE THE ECM FOR TESTING PURPOSES ) and recheck. If voltage is now normal, replace the original ECM (see ECM REPLACEMENT ). If not, check the A/C system for other symptoms.
  15. Momentarily connect main under-hood fuse/relay box 16P connector terminal No. 11 to body ground with a jumper wire several times.
    NOTE: The main under-hood fuse/relay box 14P connector is on the bottom of the fuse box. When you unbolt and invert the fuse box, leave the upper cover on it to prevent short circuits.
    Fig 4: Identifying Main Under Hood Fuse Relay Box
    G03692737Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there a clicking noise from the A/C compressor clutch? 

    1. YES -  Repair open in the wire between the ECM (A17) and the A/C clutch relay.
    2. NO -  Check the A/C system for other symptoms.
  16. Measure voltage between ECM connector terminals A27 and B20.
    Fig 5: Measuring Voltage Between ECM Connector Terminals A27 And B20
    G03692738Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there less than 1.0 V? 

    1. YES -  Substitute a known-good ECM (see HOW TO SUBSTITUTE THE ECM FOR TESTING PURPOSES ) and recheck. If the symptom/indication goes away, replace the original ECM (see ECM REPLACEMENT ). If not, inspect the A/C system for other symptoms.
    2. NO -  Repair open in the wire between the ECM (A27) and the A/C pressure switch, or between the A/C pressure switch and the heater control panel.
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