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Discussion Starter · #1 · (Edited)
Tonight I saw my first check engine light go on. I did the ACC-On, ACC-On, ACC-On trick to find the trouble code and it came out ot be "P 0645". I looked it up and found the following:

P0645 A/C Clutch Relay Circuit

Looks like my A/C relay is toast. Anyone know how this could happen? Weird....
 

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Service Manual isn't much help for the layman. Time for a visit to the dealer.

P0645-A/C CLUTCH RELAY CIRCUIT

² When Monitored:
With the ignition on. Battery voltage greater than 10 volts. A/C Switch on.
² Set Condition:
An open or shorted condition is detected in the A/C clutch relay control circuit. One Trip Fault. Three good trips to turn off the MIL.
Possible Causes
INTERNAL FUSED IGNITION SWITCH OUTPUT CIRCUIT
(C13) A/C CLUTCH RELAY CONTROL CIRCUIT OPEN
(C13) A/C CLUTCH RELAY CONTROL CIRCUIT SHORTED TO GROUND
A/C CLUTCH RELAY PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -DIAGNOSIS AND TESTING).

Diagnostic Test
1. A/C CLUTCH RELAY OPERATION
Ignition on, engine not running.
With a scan tool, actuate the A/C Clutch Relay.
Is the A/C Clutch Relay operating?
Yes >> Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No >> Go To 2

2. A/C CLUTCH RELAY RESISTANCE
Turn the ignition off.
Remove the A/C Clutch Relay from the IPM.
Measure the resistance of the A/C Clutch Relay Coil.
Is the resistance between 60 to 80 ohms?
Yes >> Go To 3
No >> Replace the A/C Clutch Relay.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)


3. INTERNAL FUSED B+ CIRCUIT
Ignition on, engine not running.
Using a 12-volt test light connected to ground, probe the Internal Fused B+ circuit in the connection.
Does the test light illuminate brightly?
Yes >> Go To 4
No >> Repair the open or short to ground in the Internal Fused B+ circuit. Check and replace any open fuses.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

4. (C13) A/C CLUTCH RELAY CONTROL CIRCUIT OPEN
Turn the ignition off.
Disconnect the PCM harness connectors.
CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform
diagnosis.
Measure the resistance of the (C13) A/C Clutch Relay Control circuit from the relay connection to the appropriate terminal of special tool #8815.
Is the resistance below 5.0 ohms?
Yes >> Go To 5
No >> Repair the open in the (C13) A/C Clutch Relay Control circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

5. (C13) A/C CLUTCH RELAY CONTROL CIRCUIT SHORTED TO GROUND
Measure the resistance between ground and the (C13) A/C Clutch Relay Control circuit at the IPM.
Is the resistance below 5.0 ohms?
Yes >> Repair the short to ground in the (C13) A/C Relay Clutch Control circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No >> Go To 6

6. PCM
NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.
Were there any problems found?
Yes >> Repair as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No >> Replace and program the Powertrain Control Module per Service Information.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
 

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maybe

may be very simple. A bunch of owners have reported the fuses loose from the factory. Go into both boxes and pull and re-seat each fuse to eliminate this possible source of failure.

In nearly 40 years of maintaining my fleet I have found many trouble codes were really wiring and connection issues. But sometimes electrical parts simply fail to operate for no apparent reason.

Good luck with your repairs.
 

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Normally this code P0645 Means theres an open to the circuit from the PCM (that controls the ac compressor) and the front fuse block (the Totally Integrated Power Module. If you suspect an open circuit check the connector going into the fuse box. Its a 16 pin green connector. If you can pull the wire out of the connector that is normally your open circuit. Its important for voltage to be on that wire for the AC Compressor to work, because thats what commands the "AC relay" on. In these vehicles there is no AC relay per say, its all controlled by the fuse box.
 

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Service Manual isn't much help for the layman. Time for a visit to the dealer.

P0645-A/C CLUTCH RELAY CIRCUIT

² When Monitored:
With the ignition on. Battery voltage greater than 10 volts. A/C Switch on.
² Set Condition:
An open or shorted condition is detected in the A/C clutch relay control circuit. One Trip Fault. Three good trips to turn off the MIL.
Possible Causes
INTERNAL FUSED IGNITION SWITCH OUTPUT CIRCUIT
(C13) A/C CLUTCH RELAY CONTROL CIRCUIT OPEN
(C13) A/C CLUTCH RELAY CONTROL CIRCUIT SHORTED TO GROUND
A/C CLUTCH RELAY PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -DIAGNOSIS AND TESTING).

Diagnostic Test
1. A/C CLUTCH RELAY OPERATION
Ignition on, engine not running.
With a scan tool, actuate the A/C Clutch Relay.
Is the A/C Clutch Relay operating?
Yes >> Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No >> Go To 2

2. A/C CLUTCH RELAY RESISTANCE
Turn the ignition off.
Remove the A/C Clutch Relay from the IPM.
Measure the resistance of the A/C Clutch Relay Coil.
Is the resistance between 60 to 80 ohms?
Yes >> Go To 3
No >> Replace the A/C Clutch Relay.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)


3. INTERNAL FUSED B+ CIRCUIT
Ignition on, engine not running.
Using a 12-volt test light connected to ground, probe the Internal Fused B+ circuit in the connection.
Does the test light illuminate brightly?
Yes >> Go To 4
No >> Repair the open or short to ground in the Internal Fused B+ circuit. Check and replace any open fuses.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

4. (C13) A/C CLUTCH RELAY CONTROL CIRCUIT OPEN
Turn the ignition off.
Disconnect the PCM harness connectors.
CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform
diagnosis.
Measure the resistance of the (C13) A/C Clutch Relay Control circuit from the relay connection to the appropriate terminal of special tool #8815.
Is the resistance below 5.0 ohms?
Yes >> Go To 5
No >> Repair the open in the (C13) A/C Clutch Relay Control circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

5. (C13) A/C CLUTCH RELAY CONTROL CIRCUIT SHORTED TO GROUND
Measure the resistance between ground and the (C13) A/C Clutch Relay Control circuit at the IPM.
Is the resistance below 5.0 ohms?
Yes >> Repair the short to ground in the (C13) A/C Relay Clutch Control circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No >> Go To 6

6. PCM
NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.
Were there any problems found?
Yes >> Repair as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No >> Replace and program the Powertrain Control Module per Service Information.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
Hey Joey, I would like to discuss this further with you. I am having this issue as well. do you have a picture of where these relays are located?
 

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Welcome aboard Crankin...
that's a 15 yo post, and Joey hasn't been here since 2011

There's a date at the top of each post... and clicking on the members avatar will let you see when they visited last.

There's a wealth of info here, but it goes back a long way. Good habit to check dates before posting to a thread. Perhaps start a fresh thread, with some details about your ride & trouble...
 

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Welcome aboard Crankin...
that's a 15 yo post, and Joey hasn't been here since 2011

There's a date at the top of each post... and clicking on the members avatar will let you see when they visited last.

There's a wealth of info here, but it goes back a long way. Good habit to check dates before posting to a thread. Perhaps start a fresh thread, with some details about your ride & trouble...
I saw it was an old post but couldn't find the info I was looking for, I have an 08 Chrysler 300 touring with a 3.5L and I can't get the AC to work. Code: P0645. I can't find the location of the AC relays. Even the dealer is unwilling to share any info. No owners manual to refer to, Is there someone you can put me in contact with or a link to a post that is a little bit more helpful?
 
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