Diagnostic Aids

Perform this test when diagnosing a symptom. To prevent replacing good components, check 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.
ECA.

Fig 1: WOT A/C Cut-Out Ckt. (Cougar & Thunderbird)

Fig 2: WOT A/C Cut-Out Ckt. (Crown Victoria, Grand Marquis & Town Car)

Fig 3: WOT A/C Cut-Out Ckt. (Escort & Tracer)

Fig 4: WOT A/C Cut-Out Circuit (Mark VII)

Fig 5: WOT A/C Cut-Out Circuit (Mustang 5.0L)

Fig 6: WOT A/C Cut-Out Circuit (All Others)

TEST PIN NO. 10 (ACCS) WIRE COLOR IDENTIFICATION

Application	Wire Color
Cougar & Thunderbird	Pink/Light Blue
Crown Victoria & Grand Marquis	Dark Green/Orange
Town Car	Pink

TEST PIN NO. 54 (WAC) WIRE COLOR ID

Application	Wire Color
Cougar & Thunderbird Except 3.8L SC	Orange/Light Blue
Crown Victoria & Grand Marquis	Dark Green/Orange
Thunderbird 3.8L SC	Pink/Yellow
Town Car	Pink

1) No A/C: Check For Voltage At 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. Turn A/C switch to A/C position. Turn blower switch to any position (Escort and Tracer).Start engine, and wait 10 seconds. Measure voltage between power side of A/C clutch wiring harness connector and negative battery terminal. If voltage is 10.5 volts or more, EEC-IV system is okay. Check A/C system. If voltage is less than 10.5 volts, go to step 2).

2) Check Continuity Of POWER-TO-CLUTCH Circuit Turn ignition off. Disconnect A/C clutch and WAC relay wiring harness connectors. Measure resistance between power side of A/C clutch wiring harness connector and POWER-TO-CLUTCH terminal at WAC relay wiring harness connector. If resistance is 5 ohms or less, reconnect A/C clutch and go to step 3). If resistance is more than 5 ohms, repair open circuit and retest system.

3) Check For Power On A/C Demand Circuit Turn ignition on. Turn A/C switch on. Set DVOM to 20-volt scale. Perform following procedure as applicable:

Escort & Tracer Turn blower motor switch to any speed. Measure voltage between A/C relay input terminal at WAC relay wiring harness connector and chassis ground.
Except Escort & Tracer Measure voltage between A/C demand input terminal at WAC relay wiring harness connector and chassis ground.

If voltage is 10.5 volts or more, go to step 5). If voltage is less than 10.5 volts for Escort and Tracer, go to step 4). For all other vehicles, verify operation of A/C clutch cycling pressure switch and A/C demand switch. If components are okay, repair open circuit and reconnect all components. Recheck system.

4) Check Continuity Between WAC Relay & A/C Relay Turn ignition off. Disconnect WAC and A/C relays. Set DVOM on 200-ohm scale. Measure resistance between A/C relay output to WAC relay circuit at A/C relay wiring harness connector and A/C relay input at WAC relay wiring harness connector. If resistance is less than 5 ohms, reconnect WAC relay and check A/C system. If resistance is 5 ohms or more, repair open circuit. Connect relays, and check system operation.

5) Check WAC Circuit For Short To Ground Turn ignition off. Disconnect 60-pin ECA connector. Disconnect WAC relay. Inspect wiring, and repair if damaged. Measure resistance between WAC terminal at WAC relay and chassis ground. If resistance is less than 10,000 ohms, repair short and recheck system operation. If resistance is 10,000 ohms or more, go to step 6).

6) Check For Voltage At ACCS Input To ECA Turn ignition off. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Set A/C switch to A/C position. Turn blower switch to any position (Escort and Tracer). Turn ignition on. Measure voltage between test pins No. 10 and 40 at breakout box. If voltage is 10.5 volts or less, repair open circuit. Connect all components, and check system operation. If voltage is more than 10.5 volts, go to step 7).

7) Check WAC Relay Turn ignition off. Connect WAC relay, leaving A/C clutch disconnected. Turn ignition on. Set A/C switch to A/C position. Turn blower switch to any position (Escort and Tracer). Measure voltage between power side of A/C clutch wiring harness connector and negative battery terminal. If voltage is 10.5 volts or more, replace ECA. If voltage is less than 10.5 volts, replace WAC relay.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 7) to step 15). No test procedures have been omitted.

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 self-test connector. Connect positive lead to positive battery terminal. Install a jumper wire between STI terminal and SIG RTN terminal at self-test connector. See Figure in CIRCUIT TEST QA. Perform KOEO SELF-TEST until continuous memory test is complete. DVOM will read less than 1.0 volt when test is complete to indicate ECA has entered OUTPUT STATE CHECK. Depress and release throttle. If voltage increases to 10.5 volts or more, remain in OUTPUT STATE CHECK and go to step 16). If voltage does not increase to 10.5 volts, depress throttle to WOT and release. If STO voltage does not go high, leave test equipment connected and go to CIRCUIT TEST QC step 2).

16) Check For VPWR To Relay With vehicle in OUTPUT STATE CHECK, disconnect wiring harness from WAC relay. Measure voltage between VPWR circuit (IGN RUN circuit for Escort and Tracer) at WAC relay wiring harness connector and chassis ground. If voltage is less than 10.5 volts, repair open in VPWR circuit between EEC power relay and WAC relay (IGN RUN circuit between WAC relay and joint box on Escort and Tracer). Remove test equipment, and retest system. If voltage is 10.5 volts or more, go to step 17).

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 circuit (IGN RUN circuit for Escort and Tracer) and connect negative test lead to WAC circuit at WAC relay wiring harness connector. Check DVOM while depressing and releasing throttle several times to cycle output on and off. If voltage cycles from high to low, replace WAC relay. If voltage does not cycle, remove test leads. Reconnect speed control servo, and go to step 18).

18) Check Continuity Of WAC Circuit Turn ignition off. Disconnect 60-pin ECA connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Measure resistance between test pin No. 54 and WAC terminal at WAC relay wiring harness connector. If reading is 5 ohms or more, repair open circuit. Reconnect all components, and retest system. If reading is less than 5 ohms, go to step 19).

19) Check WAC Circuit For Short To Power Turn ignition off. Leave ECA and WAC relay disconnected. Turn ignition on. Measure voltage between test pin No. 54 and chassis ground. If voltage is 1.0 volt or less, replace ECA and retest system. If voltage is more than 1.0 volt, repair short circuit. If symptom is still present, replace ECA.

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.

30) Cycle A/C Demand Switch Turn ignition off. Disconnect 60-pin ECA connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Connect DVOM negative test lead to test pin No. 40 and positive test lead to test pin No. 43. Turn ignition on. Cycle A/C switch. If voltage goes high and low as switch is cycled, go to step 43). If voltage does not cycle, go to step 31).

31) Check Continuity Of A/C Demand (ACD) Circuit Turn ignition off. Measure resistance between test pin No. 43 at breakout box and A/C Demand switch. If resistance is more than 5 ohms, repair open in ACD circuit and repeat QUICK TEST . If resistance is 5 ohms or less, EEC-IV system is okay. Remove breakout box, and reconnect components. Fault is in A/C system.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 31) to step 35). No test procedures have been omitted.

35) Check A/C Demand Circuit For Short To Power Turn ignition off. Disconnect WAC relay. Disconnect 60-pin ECA connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. With A/C Demand switch in OFF position, turn ignition on. Measure voltage between chassis ground and test pin No. 43 at breakout box. If voltage is 1.0 volt or less, EEC-IV system is okay. Fault is in A/C system. If voltage is more than 1.0 volt, check operation of A/C Demand switch. If switch operation is okay, repair short circuit and retest system.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 35) to step 40). No test procedures have been omitted.

Before entering this test, ensure A/C selector is in OFF position (and shift selector is in PARK position for AXOD-E and E4OD vehicles). If A/C was on, repeat QUICK TEST . If Code 67 or 79/539 is present, continue with this test.

40) Check A/C Input Code 79/539 indicates ACCS input to ECA 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 ECA connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Set DVOM to 20-volt scale. 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 . Replace ECA and repeat QUICK TEST.

41) Check For Short To Power In ECA Turn ignition off. Disconnect A/C clutch connector. Set DVOM to 20-volt scale. Turn ignition on. Measure voltage between test pins No. 10 and 40 at breakout box. If voltage is 5 volts or more, replace ECA and repeat QUICK TEST. If voltage is less than 5 volts, go to CIRCUIT TEST TD.

A low idle with A/C on may be caused by ECA not receiving or recognizing A/C input from pin No. 10

42) Check A/C Input Circuit Turn A/C switch to A/C position. For Escort, Probe and Tracer, turn blower motor switch to lowest speed. Perform KOEO SELF-TEST . If Code 67 or 79/539 is present, ECA is receiving and recognizing A/C input from pin No. 10. Check for other possible causes of low idle. If Codes 67 and 79/539 are not present, go to step 43).

43) Check A/C Input Circuit Turn ignition off. Install breakout box, leaving ECA disconnected. Set DVOM to 20-volt scale. Turn A/C on. Turn ignition on. Measure voltage between test pins No. 10 and 40. If voltage is 10.5 volts or more, replace ECA and repeat QUICK TEST . If voltage is less than 10.5 volts, repair open A/C circuit. Remove breakout box, reconnect all components and repeat QUICK TEST.