P1545

CIRCUIT DESCRIPTION
When the heater and A/C controls are in any position that enables the A/C compressor, and the A/C compressor refrigerant switch is closed, the A/C request circuit is connected to B+. The Engine Control Module (ECM) energizes the A/C compressor control circuit when a high signal voltage is detected on the A/C request circuit. The ECM will de-energize the A/C compressor control circuit during the Wide Open Throttle (WOT) maneuvers, when the Engine Coolant Temperature (ECT) exceeds a predetermined threshold or when the A/C request circuit signal voltage goes low, either by a pressure switch opening, or the HVAC system is in a non-A/C mode.

The ECM also receives an input on the A/C load signal circuit. This is accomplished through a pressure switch connected to B+ which is normally open. When the refrigerant high side pressure reaches approximately 1,200 kPa (174 psi), the switch closes sending a B+ signal to the ECM. The ECM will then raise the idle speed by approximately 50 RPM in order to help compensate for these conditions.

The ignition voltage is supplied directly to the A/C compressor control relay coil. The ECM controls the relay by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply the ground for the component being controlled. When the ECM is commanding a component ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high, near battery voltage. The relay controls the high current flow to the A/C compressor clutch. This allows the ECM driver only to have to handle the relatively low current used by the relay.

CONDITIONS FOR RUNNING THE DTC
^ The battery voltage is between 7.5-15 volts.
^ The engine speed is more than 40 RPM.
^ The A/C clutch has been requested.

CONDITIONS FOR SETTING THE DTC
ECM internal circuitry determines there is an open or a short in the A/C compressor relay control circuit.

ACTION TAKEN WHEN THE DTC SETS
The ECM will not illuminate the Malfunction Indicator Lamp (MIL).

CONDITIONS FOR CLEARING THE DTC
^ The Diagnostic Trouble Code (DTC) clears after 40 consecutive warm-up cycles in which no failures are reported by this diagnostic or any other non-emission related diagnostic.
^ The scan tool clears the DTC.

DIAGNOSTIC AIDS
If condition not present, refer to Testing for Intermittent and Poor Connections in Diagrams.

TEST DESCRIPTION

Steps 1-3:

Steps 4-17:

The number(s) below refer to the step number(s) on the diagnostic table.
3. Listen for an audible click when the A/C compressor relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
4. Tests for voltage at the coil side of the A/C compressor relay. The HEATER BLOWER fuse supplies power to the coil side of the A/C compressor relay.
5. Verifies that the ECM is providing ground to the A/C compressor relay.
6. Tests if ground is constantly being applied to the A/C compressor relay.
8. Tests if there is an internal ground in the heater and A/C controls.