Circuit Description
The PCM cycles the A/C compressor clutch in order to optimize the performance of the A/C system. The PCM determines when to cycle the A/C compressor clutch by monitoring the A/C Refrigerant Pressure sensor.
The A/C Refrigerant Pressure sensor is also used by the PCM in order to enable the cooling fans when the A/C compressor head pressure reaches a predetermine value.
The PCM energizes the A/C compressor clutch when the engine speed is less than 5000 RPM and the A/C system is requested. If you request the A/C at engine speeds greater than 5000 RPM, the PCM will not energize the A/C compressor clutch untill the engine speed decreases to less than 4895 RPM.
Any one of the following conditions disables the A/C compressor clutch.
| • | The throttle is commanded to Wide Open Throttle (WOT). |
| • | The A/C head pressure is greater than 2827 kPa (410 psi). |
| • | The A/C head pressure is less than 0 kPa (0 psi). |
| • | The ignition voltage is less than 10 volts. |
| • | The engine speed is greater than 5594 rpm. |
| • | The engine coolant temperature is greater than 125°C (257°F). |
The PCM also disables the A/C compressor when curtain DTCs set.
Diagnostic Aids
A/C Clutch Relay Underhood Electrical Center Terminal Identification | |||
|---|---|---|---|
Front of Vehicle | |||
Left Side of Vehicle | Ignition | Load | Right Side of Vehicle |
Ignition | Control | ||
Inspect the harness going to the A/C clutch and going to the PCM for intermittent connections. While the engine is operating with the A/C enabled, move related electrical connectors and harnesses. This may aid in locating an intermittent fault.
For an intermittent, refer to Symptoms .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step checks if the PCM can turn the A/C compressor ON.
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This step checks for an A/C refrigerant pressure sensor that is at a fixed value (stuck).
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Inspect the A/C clutch status circuit before replacing the A/C refrigerant pressure sensor. Also, a low refrigerant charge in the A/C system can cause a A/C system performance condition. Refer to HVAC for recharging procedure.
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Check the connections at the compressor first if the scan tool indicates that the A/C clutch is ON.
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The PCM's A/C clutch status circuit may not detect voltage when the A/C is commanded ON if the B+ supply circuit to the A/C relay is intermittent. Inspect the relay connections and operation.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
|
Important: If DTCs P0530, P1545, and P1546 are set, use those tables.
Does the A/C clutch engage? | -- | |||
Did the A/C High Side pressure increase more than the specified value when the A/C controls were turned ON? | 4 psi | Go to Diagnostic Aids | ||
|
Important: Before replacing the sensor, check the A/C system for the correct charge. An A/C system that is low on charge causes a DTC to set. Repair the faulty A/C refrigerant pressure sensor connection or replace the faulty sensor. Is the action complete? | -- | System OK | -- | |
Does the scan tool indicate the A/C clutch ON? | -- | |||
Repair the intermittent A/C clutch circuit from the A/C relay to the splice. Is the action complete? | -- | System OK | -- | |
7 |
Does the test lamp illuminate? | -- | ||
8 | Probe the A/C compressor clutch B+ supply circuit to the A/C compressor clutch ground circuit using a test lamp. Does the test lamp illuminate? | -- | ||
9 | Repair the faulty A/C clutch connection or the open A/C clutch coil. Is the action complete? | -- | System OK | -- |
10 | Repair the open or the shorted A/C clutch B+ supply circuit. Is the action complete? | -- | System OK | -- |
11 | Repair the open A/C clutch ground circuit. Is the action complete? | -- | System OK | -- |
