Diagnostic Aids

Perform this test when diagnosing a symptom. To prevent replacing good components, check the following non-EEC components and systems:

• Refrigerant charge.
• Low ambient temperature (less than 45°F). This test is only intended to diagnose:
• Wiring harness circuits (WAC, VPWR, GND, POWER-TO-CLUTCH and ACD).
• WAC relay.
• A/C fan controller.
• Faulty Powertrain Control Module (PCM).

Fig 1: WOT A/C Cut-Out Circuit (KM1 - Aerostar)

1. 1) Low/No Voltage To A/C Clutch
   
   Check all A/C-related fuses in fuse panel before proceeding with this test. Turn ignition off. Disconnect A/C clutch wiring harness connector. Disconnect WAC relay connector. Measure resistance between power side of A/C clutch harness connector and POWER-TO-CLUTCH terminal at WAC relay harness connector. If resistance is less than 5 ohms, reconnect A/C switch and go to next step. If resistance is 5 ohms or more, repair open circuit. Reconnect all components and check system operation.
2. 2) Check For Power On A/C Demand Circuit
   
   Turn ignition on. Leave WAC relay disconnected. Turn A/C switch to A/C position. Measure voltage between chassis ground and A/C DEMAND SWITCH input terminal at WAC relay wiring harness connector. If voltage is more than 10.5 volts, go to step 5). If voltage is 10.5 volts or less, verify operation of A/C clutch cycling pressure switch and A/C demand switch. If components are okay, repair open circuit and recheck system.
3. 3) Check Continuity Between WAC Relay & A/C Relay
   
   Turn ignition off. Remove WAC and A/C relay wiring harness connectors. Measure resistance between A/C RELAY terminal at WAC relay connector and A/C RELAY terminal at A/C relay connector. If resistance is less than 5 ohms, check A/C relay for low output voltage. Repair as necessary. If resistance is 5 ohms or more, repair open circuit. Connect relays, and check system operation.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 3) to step 5). No test procedures have been omitted.
4. 5) Check WAC Circuit For Short To Ground
   
   Turn ignition off. Leave WAC relay disconnected. Disconnect 60-pin PCM connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Leave PCM disconnected. Measure resistance between WAC terminal at WAC relay wiring harness connector and chassis ground. If resistance is less than 10,000 ohms, repair short and check system operation. If resistance is 10,000 ohms or more, go to next step.
5. 6) Check For Voltage At ACCS Input To PCM
   
   Turn ignition off. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Set A/C switch to A/C position. Turn ignition on. Measure voltage between test pins No. 10 and 40 at breakout box.
6. 7) Check WAC Relay
   
   Turn ignition off. Connect WAC relay, leaving A/C clutch disconnected. Leave A/C and blower switch positioned as listed in step 6). Turn ignition on. Measure voltage between POWER-TO-CLUTCH terminal of A/C clutch wiring harness connector and negative battery terminal. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, replace WAC relay. Reconnect all components and check system operation.
7. 8) Check Engine Coolant Temperature (ECT) Sensor & Throttle Position (TP) Sensor Voltage
   
   Turn ignition off. Reconnect PCM connector to breakout box. Reconnect A/C clutch connector. Turn A/C on. Start engine. Measure voltage between test pins No. 7 and 40 at breakout box. Ensure ECT sensor voltage is as specified. See ACT & ECT SENSOR SPECIFICATIONS table in CIRCUIT TEST DA. Also, measure voltage between test pins No. 40 and 47 at breakout box. With throttle plate at specified position, ensure voltage is as specified. See Figure in CIRCUIT TEST DH. If ECT sensor and TP sensor voltages are as specified, replace PCM. Remove breakout box and check system operation. If either ECT sensor or TP sensor voltage is not as specified, perform QUICK TEST. Service any codes that are present. See DIAGNOSTIC TROUBLE CODE DEFINITION CHARTS. If no codes are present, check ECT/TP sensor wiring for opens and shorts. Repair as necessary. Remove breakout box, reconnect all components, and repeat QUICK TEST.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 8) to step 15). No test procedures have been omitted.
8. 15) No A/C Output At WOT: Enter OUTPUT STATE CHECK
   
   Use only VOM or DVOM for this step. DO NOT  use scan tester. Turn ignition off. Disconnect cruise control servo wiring harness connector. Connect DVOM negative lead to STO terminal at Data Link Connector (DLC). See Fig 2 . Connect positive lead to positive battery terminal. Install a jumper wire between STI terminal and SIG RTN terminal at DLC. Perform KOEO SELF-TEST until continuous memory test is complete. DVOM will read less than 1.0 volt when test is complete to indicate PCM has entered OUTPUT STATE CHECK. Depress and release throttle. If voltage increases to more than 10.5 volts, remain in OUTPUT STATE CHECK and go to next step. If voltage does not increase to more than 10.5 volts, depress throttle to WOT and release. If STO voltage does not go high, go to CIRCUIT TEST QC, step 2).
   Fig 2: DLC Terminal ID (KM4)

   
9. 16) Check For VPWR To Relay
   
   With vehicle in OUTPUT STATE CHECK, disconnect wiring harness from WAC relay. Measure voltage between VPWR terminal at WAC relay wiring harness connector and chassis ground. If voltage is 10.5 volts or less, repair open in VPWR circuit between EEC power relay and WAC relay and retest system. If voltage is more than 10.5 volts, go to next step.
10. 17) Check WAC System For Cycling
    
    Leave vehicle in OUTPUT STATE CHECK. Disconnect WAC relay wiring harness connector. Connect DVOM positive test lead to VPWR terminal. Connect negative test lead to WAC terminal at WAC relay wiring harness connector. Check DVOM while depressing and releasing throttle several times to cycle output on and off. If voltage cycles about one volt high to low, replace WAC relay. Remove jumper wire and check system operation. If voltage does not cycle, remove test leads and jumper wire. Reconnect speed control servo, and go to next step.
11. 18) Check Continuity Of WAC Circuit
    
    Turn ignition off. Disconnect 60-pin PCM connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pin No. 54 at breakout box and WAC terminal at WAC relay wiring harness connector. If reading is 5 ohms or more, repair open circuit. Reconnect all components and check system operation. If reading is less than 5 ohms, go to next step.
12. 19) Check WAC Circuit For Short To Power
    
    Turn ignition off. Leave PCM and WAC relay disconnected. Turn ignition on. Measure voltage between test pin No. 54 and chassis ground. If voltage is less than 1.0 volt, replace PCM and retest system. If voltage is 1.0 volt or more, repair short circuit. If symptom is still present, replace PCM.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 19) to step 30). No test procedures have been omitted.
13. 30) Check A/C Input Circuit
    
    Turn A/C switch to A/C position. Perform KOEO SELF-TEST. If Code 539 is not present, go to next step. If Code 67 or Code 539 is present, PCM is receiving and recognizing A/C input from pin No. 10. Check for other possible causes of low idle.
14. 31) Check A/C Input Circuit
    
    Turn ignition off. Disconnect PCM 60-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install breakout box, leaving PCM disconnected. Turn A/C on. Turn ignition on. Measure voltage between test pins No. 10 and 40. If voltage is more than 10.5 volts, replace PCM and connect all components. Repeat QUICK TEST. If voltage is 10.5 volts or less, repair open A/C circuit. Remove breakout box, reconnect all components, and repeat QUICK TEST.
15. 32) Cycle A/C Demand Switch
    
    Turn ignition off. Disconnect PCM 60-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install breakout box, leaving PCM disconnected. Connect DVOM positive lead to test pin No. 43. Connect negative lead to test pin No. 40. Turn ignition on. Turn A/C on and off. If voltage cycles high and low when switch is cycled, EEC-IV system is okay and testing is complete. If voltage does not cycle, repair open in ACD circuit, and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 32) to step 40). No test procedures have been omitted.
NOTE: Before entering this test, ensure A/C selector is in OFF position and shift selector is in Park (A/T). If A/C was on, repeat QUICK TEST. If Code 67 or 79/539 is present, go to step 40).
16. 40) Code 67 Or 79/539: Check A/C Input
    Code 79/539 indicates ACCS input to PCM was high during SELF-TEST. Code 67 indicates Neutral Drive Switch (NDS) or ACCS circuit voltage was high during SELF-TEST. Turn ignition off. Disconnect 60-pin PCM connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Turn ignition on. Measure voltage between test pin No. 10 at breakout box and chassis ground. If voltage is 1.0 volt or more, repair short to power in A/C circuit and repeat QUICK TEST. If voltage is less than 1.0 volt, replace PCM and repeat QUICK TEST.
17. 41) Check For Short To Power In PCM
    
    Turn ignition off. Connect 60-pin PCM connector to breakout box. Ensure A/C clutch is disconnected. Turn ignition on. Measure voltage between test pins No. 10 and 40 at breakout box. If voltage is 5 volts or more, replace PCM and repeat QUICK TEST. If voltage is less than 5 volts, go to CIRCUIT TEST TD.