Pinpoint Test B: P0645

Refer to MANUAL CLIMATE CONTROL SYSTEM for schematic and connector information.

Normal Operation and Fault Conditions

Voltage is provided to the A/C clutch relay. When A/C is requested and A/C line pressures allow, a ground is provided to the A/C clutch relay coil from the PCM, energizing the A/C clutch relay.

DTC Fault Trigger Conditions

DTC	Description	Fault Trigger Condition
PCM P0645:00	A/C Clutch Relay Control Circuit: No Sub Type Information	Sets when the PCM grounds the relay circuit and more voltage than expected is detected on the relay circuit. This DTC also sets when the relay circuit is off and no voltage is detected on the relay circuit. The PCM expects to detect voltage coming through the relay coil to the relay circuit when it is not grounding it.

Possible Sources

Wiring, terminals or connectors
A/C clutch relay
PCM

Visual Inspection and Pre-checks

Inspect BJB fuses 23 (10A) and 42 (15A).

NOTE: Use the correct probe adapter(s) from the Flex Probe Kit when taking measurements. Failure to use the correct probe adapter(s) may damage the connector.

B1 CHECK THE VOLTAGE TO THE A/C (AIR CONDITIONING) CLUTCH RELAY VOLTAGE SUPPLY CIRCUITS

Ignition OFF.

Disconnect A/C clutch relay.

Ignition ON.

Measure:

Positive Lead	Measurement / Action	Negative Lead
A/C clutch relay socket 1	Courtesy of FORD MOTOR COMPANY	Ground
A/C clutch relay socket 3	Courtesy of FORD MOTOR COMPANY	Ground

Are the voltages greater than 11 volts?

Yes

GO to B2

No	VERIFY BJB fuses 42 (15A) and 23 (10A) are OK. If not OK, REFER to the OEM WIRING DIAGRAMS to identify the possible causes of the circuit short. If OK, REPAIR the circuit.

B2 CHECK THE A/C (AIR CONDITIONING) CLUTCH RELAY
- Carry out the component test on the A/C clutch relay. Refer to OEM WIRING DIAGRAMS COMPONENT TESTING for schematic and connector information.
Did the relay pass the component test?

Yes GO to B3

No INSTALL a new A/C clutch relay.

B3 CHECK THE A/C (AIR CONDITIONING) CLUTCH RELAY CONTROL CIRCUIT FOR A SHORT TO VOLTAGE

Ignition OFF.

Disconnect PCM, 2.3L C1551B, 5.0L C175B or GT 500 5.2L C1232B.

Ignition ON.

Measure:

Positive Lead	Measurement / Action	Negative Lead
A/C clutch relay socket 2	Courtesy of FORD MOTOR COMPANY	Ground

Is any voltage present?

Yes	REPAIR the circuit.

GO to B4

B4 CHECK THE A/C (AIR CONDITIONING) CLUTCH RELAY CONTROL CIRCUIT FOR A SHORT TO GROUND

Ignition OFF.

Measure:

Positive Lead	Measurement / Action	Negative Lead
A/C clutch relay socket 2	Courtesy of FORD MOTOR COMPANY	Ground

Is the resistance greater than 10, 000 ohms?

Yes

GO to B5

No	REPAIR the circuit.

B5 CHECK THE A/C (AIR CONDITIONING) CLUTCH RELAY CONTROL CIRCUIT FOR AN OPEN

Measure:

2.3L

Positive Lead	Measurement / Action	Negative Lead
A/C clutch relay socket 2	Courtesy of FORD MOTOR COMPANY	C1551B-62

5.0L

Positive Lead	Measurement / Action	Negative Lead
A/C clutch relay socket 2	Courtesy of FORD MOTOR COMPANY	C175B-19

GT 500 5.2L

Positive Lead	Measurement / Action	Negative Lead
A/C clutch relay socket 2	Courtesy of FORD MOTOR COMPANY	C1232B-19

Is the resistance less than 3 ohms?

Yes

GO to B6

No	REPAIR the circuit.

B6 CHECK FOR CORRECT PCM (POWERTRAIN CONTROL MODULE) OPERATION

Ignition OFF.

Disconnect and inspect all PCM connectors.

Repair:
- corrosion (install new connector or terminals - clean module pins)
- damaged or bent pins - install new terminals/pins
- pushed-out pins - install new pins as necessary

Reconnect all PCM connectors. Make sure they seat and latch correctly.

Operate the system and determine if the concern is still present.

Is the concern still present?

Yes	CHECK OASIS for any applicable service articles: TSB, GSB, SSM or FSA. If a service article exists for this concern, DISCONTINUE this test and FOLLOW the service article instructions. If no service articles address this concern, refer to PCM GUIDED ROUTINE TESTING

No	The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. ADDRESS the root cause of any connector or pin issues.