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Pinpoint Test O: The Air Conditioning (A/C) Is Inoperative

WARNING: This page is about a different car, the 2010 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: Before carrying out the following test, diagnose any PCM or Instrument Cluster (IC) DTCs.
NOTE: Before carrying out the following test, check that the A/C system pressure is above 290 kPa (42 psi). If the pressure is below 290 kPa (42 psi), refer to Fluorescent Dye Leak Detection .
  1. O1 CHECK THE A/C PRESSURE SENSOR (ACP_PRESS) PCM PID 
    • Key in ON position.
    • Enter the following diagnostic mode on the diagnostic tool: ACP_PRESS PCM PID
    • With the R-134a Manifold Gauge Set connected, compare the pressure readings of the manifold gauge set and the ACP_PRESS PID.
    • Are the pressure values of the R-134a Manifold Gauge Set and the ACP_PRESS PID similar? 
    1. YES  : Go to  O2.
    2. NO  : INSTALL a new A/C pressure transducer. TEST the system for normal operation.
  2. O2 CHECK THE AIR CONDITIONING SWITCH STATUS (AC_SEL_SW) HVAC PID WITH THE A/C ON 
    • Enter the following diagnostic mode on the diagnostic tool: AC_SEL_SW HVAC PID
    • Press the panel and A/C manual override buttons on the HVAC module.
    • Does the AC_SEL_SW HVAC PID read AC? 
    1. YES  : Go to  O3.
    2. NO  : Go to  O13.
  3. O3 CHECK THE AIR CONDITIONING COMPRESSOR CYCLING SWITCH (ACCS) PCM PID WITH THE A/C ON 
    • Enter the following diagnostic mode on the diagnostic tool: ACCS PCM PID
    • Press the panel and A/C manual override buttons on the HVAC module.
    • Does the ACCS PCM PID read ON? 
    1. YES  : Go to  O4.
    2. NO  : Go to  O5.
  4. O4 CHECK THE AIR CONDITIONING CLUTCH (WAC/ACCR) PCM PID WITH THE A/C ON 
    • Enter the following diagnostic mode on the diagnostic tool: WAC/ACCR PCM PID
    • Does the WAC/ACCR PCM PID read ON? 
    1. YES  : Go to  O8.
    2. NO  : Go to  O14.
  5. O5 CHECK A/C CYCLING SWITCH VOLTAGE 
    • Key in OFF position.
    • Disconnect: A/C Cycling Switch C1081
    • Key in ON position.
      • Fig 1: Measuring Voltage
      GF0014325Courtesy of FORD MOTOR CO.
    • Measure the voltage between A/C cycling switch C1081-4, circuit 1040 (RD/BK)/348 (VT), harness side and ground.
    • Is the voltage greater than 10 volts? 
    1. YES  : Go to  O6.
    2. NO  : VERIFY Central Junction Box (CJB) fuse 32 (10A) is OK. If OK, REPAIR circuit 1040 (RD/BK)/348 (VT) for an open. TEST the system for normal operation. If not OK, REFER to the SYSTEM WIRING DIAGRAMS article to identify the possible causes of the circuit short.
  6. O6 CHECK A/C CYCLING SWITCH 
    • Key in OFF position.
      • Fig 2: Measuring Resistance
      G03879157Courtesy of FORD MOTOR CO.
    • Measure the resistance between the A/C cycling switch terminals.
    • Is the resistance less than 21 ohms? 
    1. YES  : Go to  O7.
    2. NO  : INSTALL a new A/C cycling switch. TEST the system for normal operation.
  7. O7 CHECK CIRCUIT 883 (PK/LB) FOR AN OPEN 
    • Key in OFF position.
    • Disconnect: PCM C175b
      • Fig 3: Measuring Resistance
      GF0047660Courtesy of FORD MOTOR CO.
    • Measure the resistance between A/C cycling switch C1081-1, circuit 883 (PK/LB), harness side and PCM C175b-3, circuit 883 (PK/LB), harness side.
    • Is the resistance less than 5 ohms? 
    1. YES  : Go to  O14.
    2. NO  : REPAIR circuit 883 (PK/LB) for an open. TEST the system for normal operation.
  8. O8 CHECK THE VOLTAGE AT THE A/C COMPRESSOR CLUTCH FIELD COIL 
    • Key in OFF position.
    • Disconnect: A/C Compressor Clutch Field Coil C100
    • Key in ON position.
      • Fig 4: Measuring Voltage
      G04002936Courtesy of FORD MOTOR CO.
    • Measure the voltage between A/C compressor clutch field coil C100-1, circuit 321 (GY/WH), harness side and ground.
    • Is the voltage greater than 10 volts? 
    1. YES  : Go to  O9.
    2. NO  : Go to  O11.
  9. O9 CHECK THE GROUND AT THE A/C COMPRESSOR CLUTCH FIELD COIL 
      Fig 5: Measuring Voltage
      GF0014330Courtesy of FORD MOTOR CO.
    • Measure the voltage between A/C compressor clutch field coil C100-2, circuit 57 (BK), harness side and A/C compressor clutch field coil C100-1, circuit 321 (GY/WH), harness side.
    • Is the voltage greater than 10 volts? 
    1. YES  : Go to  O10.
    2. NO  : REPAIR circuit 57 (BK). TEST the system for normal operation.
  10. O10 CHECK THE A/C COMPRESSOR CLUTCH AIR GAP 
      Fig 6: Measuring Clutch Air Gap
      GF0004396Courtesy of FORD MOTOR CO.
    • Measure the A/C compressor clutch air gap at 3 equally spaced locations between the clutch hub and the A/C compressor clutch pulley.
    • Is the A/C compressor clutch air gap greater than 0.65 mm (0.026 in)? 
    1. YES  : ADJUST the A/C compressor clutch gap. REFER to Air Conditioning (A/C) Clutch Air Gap Adjustment . TEST the system for normal operation.
    2. NO  : INSTALL a new A/C compressor clutch field coil. REFER to CLIMATE CONTROL article. TEST the system for normal operation.
  11. O11 CHECK CIRCUIT 1810 (LG/OG) FOR AN OPEN 
    • Key in OFF position.
    • Disconnect: A/C Clutch Relay
    • Key in ON position.
      • Fig 7: Measuring Voltage
      GF0018878Courtesy of FORD MOTOR CO.
    • Measure the voltage between A/C control relay socket pin 3, circuit 1810 (LG/OG) and ground.
    • Is the voltage greater than 10 volts? 
    1. YES  : Go to  O12.
    2. NO  : VERIFY Battery Junction Box (BJB) fuse 11 (15A) is OK. If OK, REPAIR circuit 1810 (LG/OG) for an open. TEST the system for normal operation. If not OK, REFER to the SYSTEM WIRING DIAGRAMS article to identify the possible causes of the circuit short.
  12. O12 CHECK CIRCUIT 321 (GY/WH) FOR AN OPEN 
    • Key in OFF position.
      • Fig 8: Measuring Resistance
      GF0018879Courtesy of FORD MOTOR CO.
    • Measure the resistance between A/C control relay socket pin 5, circuit 321 (GY/WH) and A/C compressor clutch field coil C100-1, circuit 321 (GY/WH), harness side.
    • Is the resistance less than 5 ohms? 
    1. YES  : CARRY OUT the A/C clutch relay component test. Refer to COMPONENT TESTING article. If the relay tests OK, go to  O14.
    2. NO  : REPAIR circuit 321 (GY/WH) for an open. TEST the system for normal operation.
  13. O13 CHECK HVAC MODULE CONNECTION 
    1. YES  : INSTALL a new HVAC module. REFER to CLIMATE CONTROL article. TEST the system for normal operation.
    2. NO  : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  14. O14 CHECK PCM CONNECTION 
    • Clear the DTCs.
    • Disconnect all of the PCM connectors.
    • Check for:
      • corrosion.
      • pushed-out pins.
      • incorrectly seated connector.
    • Connect and correctly seat all of the PCM connectors.
    • Operate the system.
    • Does the concern return? 
    1. YES  : INSTALL a new PCM. TEST the system for normal operation.
    2. NO  : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.
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