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).
Power for fan motors comes from a fusible link at battery junction block. Relays are energized when current flows form FANS/ACTUATOR fuse through relay coils to ground through PCM. PCM Output Driver Module (ODM) "B" output No. 1 is grounded for low speed fan operation. PCM ODM "B" outputs No. 1 and 2 are grounded for high speed operation.
Cooling fan system consists of a single-speed (right side) cooling fan and a dual-speed (left side) cooling fan. While in low speed (fan No. 1) operation, Light Blue wire supplies a feed directly to right side cooling fan motor. Left side cooling fan motor is supplied a feed through a resistor, causing it to run at low speed. When high speed (fan No. 2) operation is commanded, right side fan continues to run at low speed, but Black wire supplies a feed directly to left side cooling fan motor, causing it to run at high speed.
PCM commands low speed fans operation when vehicle speed is less than 58 MPH, coolant temperature is greater than 212°F (100°C), vehicle speed is less than 40 MPH, intake air temperature is greater than 48°F (9°C), and A/C refrigerant pressure is greater than 190 psi (13.4 kg/cm 2 ).
High speed fan operation is commanded when vehicle speed is less than 65 MPH and engine coolant is greater than 226°F (108°C), or vehicle speed is less than 50 MPH and A/C refrigerant pressure is greater than 260 psi (18.3 kg/cm 2 ).
See also:
• K - SENSOR RANGE CHARTS