DTC P0645: A/C CLUTCH RELAY CIRCUIT Dodge Ram Van B2500

Note. For connector terminal identification, see CONNECTOR IDENTIFICATION . For circuit identification and wiring diagram, see RAM VAN & RAM WAGON wiring diagram in WIRING DIAGRAMS article.

Note. DTC P0645: A/C CLUTCH RELAY CIRCUIT is monitored with ignition switch in RUN position and battery voltage more than 10.4 volts. DTC may be stored in Powertrain Control Module (PCM) when PCM senses an open or short in A/C clutch relay control circuit. Possible causes are: defective A/C clutch relay, defective PCM, defective connector or defective wiring.

1. Turn ignition on, with engine off. Using scan tool, actuate A/C clutch relay. A/C clutch relay is located in Power Distribution Center (PDC). PDC is located next to battery. Refer to label under PDC cover for relay location. If A/C clutch relay clicks, go to next step. If A/C clutch relay does not click, go to step 4).
2. Ensure ignition is on, with engine off. Wiggle wiring harness from A/C clutch relay to PCM while actuating A/C clutch relay. PCM is located in engine compartment. See PCM LOCATION table under SYSTEM DIAGNOSTICS. If A/C clutch relay stops clicking at any time while wiggling wiring harness, repair wiring harness where wiggling caused A/C clutch relay to stop clicking. Perform TEST VER-2A. If A/C clutch relay does not stop clicking at any time while wiggling wiring harness, go to next step.
3. Turn ignition off. Visually inspect related connectors and wiring harness. Repair connectors and wiring harness as necessary. Perform TEST VER-2A. If connectors and wiring harness are okay, test is complete.
4. Turn ignition off. Remove A/C clutch relay. A/C clutch relay is located in Power Distribution Center (PDC). PDC is located next to battery. Refer to label under PDC cover for relay location. Clean and/or repair connector as necessary. Using an ohmmeter, check resistance between A/C clutch relay terminals No. 85 and 86. If resistance is less than 100 ohms, go to next step. If resistance is 100 ohms or more, replace A/C clutch relay. Perform TEST VER-2A.
5. Ensure ignition is off. Ensure A/C clutch relay is still removed. Turn ignition on, with engine off. Using a 12-volt test light connected to ground, probe A/C clutch relay connector, fused ignition switch output circuit (Red/Yellow wire). If test light illuminates brightly, go to next step. If test light does not illuminate brightly, repair open or high resistance in fused ignition switch output circuit. Perform TEST VER-2A.
6. Ensure ignition is off. Ensure A/C clutch relay is still removed. Disconnect PCM connectors. PCM is located in engine compartment. See PCM LOCATION table under SYSTEM DIAGNOSTICS. Clean and/or repair connectors as necessary. Using an ohmmeter, check resistance of A/C clutch relay control circuit (Dark Blue/Orange wire) between A/C clutch relay and PCM. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open A/C clutch relay control circuit. Perform TEST VER-2A.
7. Ensure ignition is off. Ensure A/C clutch relay and PCM connectors are still disconnected. Using ohmmeter, check resistance between ground and PCM connector, A/C clutch relay control circuit (Dark Blue/Orange wire). If resistance is less than 5 ohms, repair A/C clutch relay control circuit for short to ground. Perform TEST VER-2A. If resistance is 5 ohms or more, go to next step.
8. At this time, PCM is assumed to be defective. Replace PCM. Perform TEST VER-2A.