Diagnostic Aids

Perform this test when instructed during QUICK TEST or other test step. This test is intended to diagnose the following:

• A/C relay.
• High pressure switch.
• ACR and HPS harness circuits.
• PCM.

1. 1) Check Power A/C To Relay
   
   Turn ignition off. Disconnect A/C relay. Turn ignition on. Measure voltage of PWR circuit at A/C relay harness connector. See Fig 1. If voltage is greater than 10 volts, go to next step. If voltage is not greater than 10 volts, repair open in circuit. Reconnect all electrical connections and repeat QUICK TEST .
   Fig 1: Identifying A/C Relay Circuit & Harness Connector

   Courtesy of FORD MOTOR CO.
2. 2) Perform Relay Click Test
   
   Install relay. Turn ignition off. Disconnect PCM harness connector and inspect for damage. Turn ignition on. Ground ACR circuit at PCM harness connector. See CIRCUIT PIN IDENTIFICATION  table. If relay does not click, go to next step. If relay clicks when grounded, replace PCM.
3. 3) Check ACR Circuit For Open
   
   Remove relay. Measure resistance of ACR circuit between A/C relay harness connector and PCM harness connector. If resistance is less than 5 ohms, go to next step. If resistance is not less than 5 ohms, repair open ACR circuit.
4. 4) Check ACR Circuit For Short
   
   Measure resistance between ground and ACR relay circuit at PCM harness connector. Figure and Fig 1 . If resistance is greater than 10 k/ohms, replace relay. If resistance is not greater than 10 k/ohms, repair short in circuit.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 4)  to step 10)  . No test procedures have been omitted.
5. 10) Check Ground At A/C High Pressure Switch
   
   Disconnect A/C high pressure switch. Measure resistance between GND terminal at switch harness connector and chassis ground. See Fig 2. If resistance is less than 5 ohms, go to next step. If resistance is not less than 5 ohms, repair open in ground circuit.
   Fig 2: Identifying High Pressure Switch Circuits & Harness Connector

   Courtesy of FORD MOTOR CO.
6. 11) Check Signal Circuit For Open
   
   Measure resistance of PCM REF circuit between PCM harness connector and A/C switch harness connector. If resistance is less than 5 ohms, go to next step. If resistance is not less than 5 ohms, repair open in circuit.
7. 12) Check Signal Circuit To PCM For Short
   
   Measure resistance between PCM REF circuit at PCM harness connector and ground. If resistance is greater than 10 k/ohms, go to next step. If resistance is not greater than 10 k/ohms, repair short to ground in circuit.
8. 13) Check A/C High Pressure Switch
   
   See appropriate A/C-HEATER SYSTEMS - VILLAGER article in lemon-25® AIR CONDITIONING & HEATING manual for switch testing procedures. Replace switch as necessary. If switch tests okay and no problem is found with circuit, replace PCM.