PCM Controlled A/C Circuit Diagnosis

Diagnostic Chart:

CIRCUIT DESCRIPTION
When an A/C mode is selected, the A/C control head or the A/C programmer supplies a 12 volt signal to the PCM A/C request input. The A/C compressor clutch relay is controlled by the PCM. The PCM provides a ground path for the A/C relay coil. When the A/C compressor relay is engaged battery voltage is supplied to the compressor clutch coil. The PCM will enable the A/C compressor clutch whenever the engine is running and the A/C has been requested unless one or more of the following conditions are present:
^ The throttle angle is more than 90 percent.
^ The A/C head pressure is more than 414 psi (4.27 volts) or less than 34 psi (0.35 volt) as determined by the A/C refrigerant pressure sensor.
^ The ignition 1 voltage is less than 10 volts.
^ The engine speed is more than 4225 RPM for more than 5 second.
^ The engine speed is more than 5280 RPM for any amount of time.
^ The engine coolant temperature (ECT) is more than 125°C (257°F).
^ The intake air temperature (IAT) is less than 0°C (32°F).

Any of the conditions described above will inhibit A/C compressor relay operation.