05.08.2005, 20:53
Hallo Michael,
GENERAL DESCRIPTION
The electric cooling fan(s) are used to cool engine coolant flowing through the radiator. They are also used to cool the refrigerant flowing through the A/C condenser.
OPERATION
The electric cooling fan(s) are controlled by the PCM. The PCM controls the ground path for the three cooling fan relays. The relays are used to control the high current flow to power the cooling fan motors. Both fans operate together. When minimum cooling is required, the PCM energizes cooling fan relay #1 and both fans operate at low speed, since the fans are connected in series through cooling fan relay #3, and cooling fan relay #2 is open. When maximum cooling is required, the PCM energizes all three cooling fan relays. The left fan is still powered through cooling fan relay #1, but is now grounded through cooling fan relay #3. The right fan is now powered directly through cooling fan relay #2 and both fans operate at high speed.
Low Speed Fans
The cooling fans are controlled by the PCM based on inputs from the A/C System, Engine Coolant Temperature (ECT) sensor and Vehicle Speed Sensor (VSS).
The PCM will command low speed fans "ON" when Engine Coolant Temperature (ECT) is above 108°C (226°F). The PCM will turn the fans "OFF" when the temperature drops about 3°C (5°F). The minimum "ON" time for low speed fans is 50 seconds.
High Speed Fans
The PCM will command high speed fans "ON" when any of the following conditions exist at idle.
• Certain Diagnostic Trouble Codes (DTCs) set.
• ECT above 113°C (235°F).
• A/C head pressure above 248 psi.
If the high speed fans were turned "ON" by the ECT, the PCM will switch the fans back to low speed when the temperature drops about 3°C (5°F). Minimum "ON" time for HI speed fans is 30 seconds.
Quelle: GM 1995 Service Manual Book 2 (Seite 6E3-C12-1)
GENERAL DESCRIPTION
The electric cooling fan(s) are used to cool engine coolant flowing through the radiator. They are also used to cool the refrigerant flowing through the A/C condenser.
OPERATION
The electric cooling fan(s) are controlled by the PCM. The PCM controls the ground path for the three cooling fan relays. The relays are used to control the high current flow to power the cooling fan motors. Both fans operate together. When minimum cooling is required, the PCM energizes cooling fan relay #1 and both fans operate at low speed, since the fans are connected in series through cooling fan relay #3, and cooling fan relay #2 is open. When maximum cooling is required, the PCM energizes all three cooling fan relays. The left fan is still powered through cooling fan relay #1, but is now grounded through cooling fan relay #3. The right fan is now powered directly through cooling fan relay #2 and both fans operate at high speed.
Low Speed Fans
The cooling fans are controlled by the PCM based on inputs from the A/C System, Engine Coolant Temperature (ECT) sensor and Vehicle Speed Sensor (VSS).
The PCM will command low speed fans "ON" when Engine Coolant Temperature (ECT) is above 108°C (226°F). The PCM will turn the fans "OFF" when the temperature drops about 3°C (5°F). The minimum "ON" time for low speed fans is 50 seconds.
High Speed Fans
The PCM will command high speed fans "ON" when any of the following conditions exist at idle.
• Certain Diagnostic Trouble Codes (DTCs) set.
• ECT above 113°C (235°F).
• A/C head pressure above 248 psi.
If the high speed fans were turned "ON" by the ECT, the PCM will switch the fans back to low speed when the temperature drops about 3°C (5°F). Minimum "ON" time for HI speed fans is 30 seconds.
Quelle: GM 1995 Service Manual Book 2 (Seite 6E3-C12-1)
