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 A/C compressor clutch coil.
PCM will enable A/C compressor clutch whenever engine is running and A/C has been requested, unless
- Throttle angle is greater than 90 percent.
- A/C head pressure is greater than 414 psi (29.1 kg/cm 2 ).
- A/C head pressure is less than 35 psi (2.5 kg/cm 2 ).
- Ignition voltage is less than 10.5 volts.
- Engine speed is greater than 4500 RPM for 5 seconds.
- Engine coolant temperature is greater than 257°F (125°C).
- Intake air temperature is less than 41°F (5°C).
Power for cooling fan motors is supplied through COOL FAN 1 Maxi-fuse (30-amp) and COOL FAN 2 Maxi-fuse (30-amp) in underhood electrical center. Cooling fan relays are energized when current flows from Maxi-fuses through relay coils, then to ground through Powertrain Control Module (PCM). No. 1 cooling fan relay control circuit is grounded for low speed operation. Both fan control circuits and all 3 relays are grounded for high speed fan operation.
During low speed fan operation, PCM supplies a ground path for No. 1 cooling fan relay. As a result, relay contacts close, allowing current to flow from COOL FAN 1 Maxi-fuse through relay coil to cooling fan No. 1 (left side). During low speed operation, ground path for cooling fan No. 1 is through cooling fan relay (5-pin) and cooling fan motor No. 2 (right side). This results in a series circuit with both fans operating at low speed.
During high speed fan operation, PCM supplies 2 ground paths for all 3 cooling fan relays. As a result, relay contacts close in all relays, allowing both cooling fan motors to operate at high speed. Both cooling fans are supplied current from both COOL FAN Maxi-fuses. Each cooling fan motor has a separate ground path when operating in high speed mode.