DESCRIPTION & OPERATION
To improve idle quality and Wide Open Throttle (WOT) performance, and for system protection, the A/C compressor clutch is controlled by the Powertrain Control Module (PCM).
A refrigerant pressure sensor is used to indicate high and low side refrigerant pressure to the PCM for controlling cooling fan, A/C compressor clutch and Idle Air Control (IAC) valve. If a fault is detected in refrigerant pressure circuit, A/C compressor clutch will be disabled.
The A/C compressor clutch relay is controlled by the PCM. This allows the PCM to raise idle speed before engaging compressor clutch, and disable compressor clutch during WOT, high engine RPM, high power steering loads and hot engine restarts. PCM also disables compressor clutch if coolant temperature becomes excessive.
Description
When A/C is selected a 12-volt signal is supplied to A/C request input of PCM. A/C compressor clutch relay is controlled through PCM. PCM monitors A/C refrigerant pressure. If A/C refrigerant pressure, and engine operating conditions are within a specific calibrated acceptable range, PCM will enable A/C compressor relay. This is done by providing a ground path for A/C relay coil within PCM. When A/C compressor relay is enabled, battery voltage is supplied to compressor clutch coil.
PCM will enable A/C compressor clutch whenever engine is running and A/C has been requested, unless throttle is greater than 90 percent, A/C head pressure is greater than 414 psi (29.1 kg/cm 2 ) or 4.27 volts, or less than 34 psi (2.3 kg/cm 2 ), or .35 volt as determined by A/C refrigerant pressure sensor, ignition voltage less than 10.5 volts, engine speed greater than 4500 RPM for 5 seconds, engine coolant temperature greater than 257°F (125°C), and intake air temperature less than 41°F (5°C).