AC Diagnostic
Below is a diagnostic that may help you locate the open or bad connection
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HVAC Compressor Clutch Does Not Engage
A/C Compressor Clutch Does Not Engage <> Step
Action
Value(s)
Yes No
DEFINITION: A/C compressor clutch will not engage when an A/C request has been made
and no Powertrain DTC are set.
1
Were you sent here from the HVAC Blower Controls System Check (C60)?
-Go to Step 2
Go to HVAC Blower Controls System Check (C60)
2
Remove the A/C CLU Micro Relay #34.
Disconnect the A/C compressor clutch connector.
Using a DMM, measure for continuity between terminal A of
the A/C compressor clutch connector and ground.
Is the resistance infinite?
-Go to Step 4
Go to Step 3
3
Locate and repair a short to ground in CKT 59 between the underhood electrical center and
the A/C compressor clutch connector.
Is the repair complete?
-Go to HVAC Blower Controls System Check (C60)
-4
A/C CLU Micro Relay #34 still removed.
A/C compressor clutch connector still disconnected.
Connect a fused jumper between terminal 30 and terminal 87 of the underhood electrical
center which is used for the A/C CLU Micro Relay #34.
Using a DMM, measure the voltage at the A/C compressor clutch connector terminal A.
Is the voltage within the specified values?
10.0-14.0V
Go to Step 6
Go to Step 5
5
Locate and repair an open or a high resistance in CKT 59.
Is the repair complete?
-Go to HVAC Blower Controls System Check (C60)
-6
Using a DMM, measure for continuity between terminal B of
the A/C compressor clutch connector and ground.
Is the CKT 150 continuous to ground?
-Go to Step 8
Go to Step 7
7
Locate and repair an open or a high resistance in CKT 150.
Is the repair complete?
-Go to HVAC Blower Controls System Check (C60)
-8
Disconnect the powertrain control module (PCM) connector C1.
Reinstall the A/C CLU Micro Relay #34.
Connect a fused jumper between the PCM connector C1 terminal 39 and ground.
Turn the ignition switch to the ON position.
Using a DMM, measure the voltage at the A/C compressor clutch connector terminal A.
Is the voltage within the specified values?
10.0-14.0V
Go to Step 9
Go to Step 10
9
Remove the fused jumper from the PCM connector C1 terminal 39 and ground.
Reconnect the A/C compressor clutch connector.
Reinstall the fused jumper between the PCM connector C1 terminal 39 and ground.
Turn the ignition switch to the ON position.
Does the A/C compressor clutch engage?
-Go to System Performance Test
Go to Step 16
10
Turn the ignition switch to the OFF position.
Remove the A/C CLU Micro Relay #34.
Using a DMM, measure for continuity between the PCM connector C1 terminal 39 and
terminal 88 of the underhood electrical center which is used for the A/C CLU Micro Relay
#34.
Is CKT 459 continuous between these two terminals?
-Go to Step 12
Go to Step 11
11
Locate and repair an open or a high resistance in CKT 459.
Is the repair complete?
-Go to HVAC Blower Controls System Check (C60)
-12
Replace the A/C CLU Mini Relay #34 and retest the A/C system.
Does replacing the A/C CLU Mini Relay #34 correct the concern?
-Go to HVAC Blower Controls System Check (C60)
Go to Step 13
13
Disconnect the HVAC control head connector C1.
Connect a DMM between the PCM connector C1 terminal 47 and the HVAC control head
connector C1 terminal B.
Measure CKT 762 for continuity between these two connectors.
Is CKT 762 continuous?
-Go to Step 15
Go to Step 14
14
Locate and repair an open or a high resistance in CKT 762.
Is the repair complete?
-Go to HVAC Blower Controls System Check (C60)
-15
Connect a DMM between the PCM connector C1 terminal 47 and ground.
Measure CKT 762 for continuity to ground.
Is CKT 762 continuous to ground?
-Go to Step 16
Go to Step 17
16
Locate and repair a short to ground in CKT 762.
Is the repair complete?
-Go to HVAC Blower Controls System Check (C60)
-17
Disconnect the DMM.
Reconnect all connectors back to their respective modules.
Install the scan tool to the diagnostic link connector.
Start the engine and allow it to idle in Park.
Select the area of the scan tool which will read HVAC button output status.
Depress the A/C button on/off several times.
Does the scan tool read the A/C request being sent by the HVAC control head?
-Go to Step 18
Go to Step 19
18
Replace the PCM.
Is the repair complete?
-Go to HVAC Blower Controls System Check (C60)
-19
Replace the HVAC control head.
Is the repair complete?
-Go to HVAC Blower Controls System Check (C60)
Hi, below is a description of your system. from the codes listed it seems the compressor is
not getting the voltage neccessary to engage it.
Most probable is disengaged connnector somewhere in the circuit, or possible a bad relay. I
believe the relay and the fuse are located in the engine bay fuse block. But look for a bad
connection, because that would make sense, if the tuner moved something around while
working possibly near the #7 plug which is hard to access.
Read Below
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Circuit Operation
The compressor for the air conditioning system is belt-driven by the engine through
the A/C Compressor Clutch. The Powertrain Control Module (PCM) controls
the A/C Compressor depending on the HVAC Programmer Module mode and temperature
settings. The PCM controls theA/C Compressor Clutch by activating the A/C CLU micro
relay 34.
When the PCM receives a A/C request from the HVAC Programmer Module
through circuit 762, it activates the A/C CLU micro relay 34through circuit 459. The
battery voltage is applied from the A/C mini fuse 24 and A/C micro relay 34 to
the A/C Compressor Clutchthrough circuit 59. Circuit 59 also carries
the A/C Compressor status to the PCM. The A/C Diode prevents current flow that could
damageA/C Compressor Clutch components. The A/C Compressor Clutch is grounded
through circuit 150 to Splice Pack #100, SP100.
The PCM uses the A/C Refrigerant Pressure Sensor to control refrigerant pressure. If the
refrigerant pressure is too high (i.e., could cause engine overheating), the PCM disengages
the A/C Compressor Clutch. The A/C Refrigerant Pressure Sensor sends refrigerant
pressure data to the PCM through circuit 380. Circuit 407 supplies the A/C Refrigerant
Pressure Sensor with ground voltage, and circuit 474 supplies 5V reference voltage.