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Engine System Testing & Engine Component Testing - 3.1L: Overview Oldsmobile Cutlass VI

Testing & Diagnostics ~392 words

Description

When A/C is selected through A/C control head, 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 accomplished by providing a ground path for A/C relay coil with 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

  1. Throttle angle is greater than 90 percent.
  2. A/C head pressure is greater than 414 psi (29.1 kg/cm 2 ).
  3. A/C head pressure is less than 35 psi (2.5 kg/cm 2 ).
  4. Ignition voltage is less than 10.5 volts.
  5. Engine speed is greater than 4500 RPM for 5 seconds.
  6. Engine coolant temperature is greater than 257°F (125°C).
  7. Intake air temperature is less than 41°F (5°C).

Power for cooling fan motors is supplied through underhood electrical center. Cooling fan relays are energized when current flows from COOL FAN fuse No. 1 (30-amp) and COOL FAN fuse No. 2 (15-amp) in underhood electrical center, then through relay coils 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 underhood electrical center through relay to cooling fan motor No. 1 (left side). During low speed operation, ground path for cooling fan No. 1 is through No. 2 cooling fan relay 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 a ground path 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 underhood electrical center. Each cooling fan has a separate ground path when operating in high speed mode.

See also:
• ADJUSTMENTS - 3.1L

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