With Manual AC

CIRCUIT DESCRIPTION
The A/C system uses an A/C refrigerant pressure sensor mounted in the high pressure side of the A/C refrigerant system to monitor A/C refrigerant pressure. The powertrain control module (PCM) uses this information to turn ON the engine coolant tans when the A/C refrigerant pressure is high and to keep the compressor disengaged when A/C refrigerant pressure is excessively high or low. The A/C refrigerant pressure sensor operates like other 3 wire sensors. The PCM applies a 5 volt reference and a sensor ground to the sensor. Changes in the A/C refrigerant pressure will cause the A/C refrigerant pressure input to the PCM to vary. The PCM monitors the A/C refrigerant pressure sensor signal circuit. The PCM sends the A/C pressure data to the dash integration module (DIM) over the class 2 serial data circuit. The DIM will not request A/C compressor clutch engagement if the A/C pressure is too high and set DTC P1540.

CONDITIONS FOR RUNNING THE DTC
The DIM must be powered.

CONDITIONS FOR SETTING THE DTC
The A/C refrigerant pressure is greater than 2968 kPa (430 psi) for more than 500 milliseconds.

ACTION TAKEN WHEN THE DTC SETS
The DIM disables the A/C clutch.

CONDITIONS FOR CLEARING THE DTC
^ When the A/C refrigerant pressure drops to less than 1386 kPa (201 psi) the DIM will clear the current DTC and go to a history DTC. If A/C is still requested, the DIM will then enable the A/C clutch.
^ The history DTC will clear after 40 ignition cycles.
^ Use a scan tool in order to clear the DTC.

DIAGNOSTIC AIDS
^ If DTC P1540 is stored as a history code it indicates that the DIM did receive a high A/C refrigerant pressure message from the PCM. This code could also be caused by an intermittent short to voltage on the A/C refrigerant pressure sensor signal circuit which would cause the PCM to set DTC P0530. The code could be the result of an actual A/C refrigerant over-pressure condition.
^ It is possible for the refrigerant system pressure to exceed 2968 kPa (430 psi) during extended engine idle speed with A/C ON when ambient temperatures are greater than 41°C (105°F). This could be caused by the following conditions:
- An overcharged A/C system
- A failed A/C refrigerant pressure sensor
- Blockage in a refrigerant line
- Debris in front of the A/C condenser
- Radiator or A/C condenser air shields missing or out of location
- Inoperative engine cooling fans
- Extended periods at idle in city traffic followed by rapid acceleration
- Aftermarket products affecting cooling system performance
^ If the concern is intermittent, refer to Testing for Intermittent and Poor Connections in Diagnostic Aids.

TEST

Steps 1-5: