cooling fan ?
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Racer
Joined: Feb 2006
Posts: 388
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From: Moscow pa
cooling fan ?
I have a 90 pretty much all stock.I know the two fans should come on with the ac on but i have only ever had the one on the drivers side come on never both. where do i start to look and how can i test the fan to make sure it's working.Car getts pretty warm in slow traffic and don't want to cook it thanks for the help Tbone
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 207
From: Orlando FL
I don't know how a 90 is configured, I a have a 94. My drivers side fan comes on with my A/C and the other aux fan on pass side at 239 according to book. Except I added some wiring and a switch to make it turn on when I feel like it. Other wise you would need a wiring diagram to locate the proper relay, and check it, put 12 volts external into fan to run it and to check out override switch it it has one. Unless you get over 239 its not coming on. Take this info with a grain of salt for your exact vett. The Helms book for my 94 says this, the Haynes book (84 - 96) also says it should operate this way for 88 and later models. So I think this correct. Good luck 
Burning Brakes
Joined: Jun 2004
Posts: 752
Likes: 0
From: richardson tx
see if this helps
1990 ENGINE COOLING General Motors Corp. - Electric Cooling Fan
APPLICATION
ELECTRIC COOLING FAN APPLICATIONS
Application Engine
"Y" Body 5.7L
DESCRIPTION
All FWD and some RWD vehicles use an electric cooling fan. This fan is used for engine and A/C condenser cooling and operates when A/C is on and if engine overheats.
OPERATION
All electric cooling fans operate when engine coolant temperature exceeds a certain value. The ECM completes ground path for the cooling fan relay. Relay contacts then close and complete circuit between fusible link and fan motor. When the engine cools, the switch opens and fan stops. If coolant sensor fails, the ECM will command constant fan operation.
A/C equipped vehicles have a separate signal line to the ECM for fan control. When A/C control switch is "ON", and A/C system low pressure switch is closed, the ECM receives a signal on this line and turns on the cooling fan. The compressor clutch does not have to engage for ECM to turn fan on.
On some models, when engine is off, ECM may turn on the fan relay and run fan for up to 7 minutes. This occurs if hot conditions were present while engine was running. Hot conditions are based on Manifold Absolute Temperature (MAT) signal to ECM, coolant temperature and time from start.
TROUBLE SHOOTING
NOTE: This article contains test charts that are part of General Motors Computerized Engine Controls. Only those charts required to test electric cooling fans are included. Other diagnostic codes may appear while performing electric cooling fan diagnosis. For complete information on General Motors Computerized Engine Control systems, see appropriate article in ENGINE PERFORMANCE section.
CHART C-12, COOLING FAN
Two cooling fans are used, primary fan (driver's side) and secondary fan (passenger's side). Independent fans are controlled by the ECM based on air conditioner head pressure, coolant temperature, engine oil temperature, vehicle speed and A/C operation.
Primary cooling fan is totally controlled by ECM based on inputs from A/C operation, coolant temperature sensor and vehicle speed sensor. Primary cooling fan will be on in the following conditions:
A/C operation exists with high A/C pressure.
A/C operation exists with high A/C pressure and vehicle speed less than 35 mph and coolant temperature is greater than 226°F (108°F).
A/C operation does not exist, vehicle speed greater than 35 mph and coolant temperature is greater than 226°F (108°F).
Primary cooling fan will shut off when the following conditions have existed for 20 seconds:
A/C operation exists with high A/C pressure, vehicle speed is less than 35 mph and coolant temperature is less than 221°F (105°F).
A/C operation does not exist, vehicle speed is greater than 35 mph and coolant temperature is less than 221°F (105°F).
Secondary cooling fan is controlled by the ECM based on inputs from coolant temperature sensor and vehicle speed sensor. ECM will activate secondary cooling fan if primary cooling fan has been operating for 2 seconds and the following conditions exist:
A/C operation exists with high A/C pressure and vehicle speed is less than 50 mph.
A/C operation exists with high A/C pressure, vehicle speed is less than 35 mph and coolant temperature is greater than 235°F (113°F).
A/C operation does not exist, vehicle speed is greater than 35 mph and coolant temperature is greater than 235°F (113°F).
Secondary cooling fan will shut off when the following conditions exist for 15 seconds:
A/C operation exists with high A/C pressure, vehicle speed is less than 35 mph and coolant temperature is less than 226°F (108°F).
A/C operation does not exist, vehicle speed is greater than 35 mph and coolant temperature is less than 226°F (108°F).
Battery voltage is supplied to the fan relay on terminal "E" and ignition voltage to terminal "D."
Grounding circuit No. 409 (relay terminal "F") energizes the primary cooling fan relay and supplies battery voltage to the primary cooling fan motor. Grounding circuit No. 473 (relay terminal "F") energizes the secondary cooling fan relay and supplies battery voltage to the secondary cooling fan motor.
The A/C cooling fan control switch (mounted in the A/C high pressure line) will close when head pressure exceeds 240 psi (16.8 kg/cm2 ). This input causes the ECM to ground circuit No. 409 or 473 if other requirements are met. If a Code 14, 15, 52 or 62 exists, or the ECM is operating in the fuel back-up mode, the ECM will turn on the cooling fans. Cooling fan relays are located on upper radiator support in front of the left wheel panel.
Diagnostic Aids
If an overheating condition is suspected, verify if this is due to actual boilover. If gauge or light indicates an overheat condition, and no boilover is in evidence, inspect the gauge/light circuit for malfunction.
If vehicle is overheating and the gauge or light indicates the same, but the cooling fan is not coming on, check the coolant sensor temperature using a "SCAN" tester. Sensor may have shifted calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system.
Fig. 1: Cooling Fan Circuit Diagram
Courtesy of GENERAL MOTORS CORP.
Fig. 2: Cooling Fan Flow Chart (1 of 2)
Courtesy of GENERAL MOTORS CORP.
Fig. 3: Cooling Fan Flow Chart (2 of 2)
Courtesy of GENERAL MOTORS CORP.
CHART C-10, A/C CLUTCH CIRCUIT
The A/C clutch control relay is ECM controlled to delay A/C clutch engagement approximately 4 tenths of a second after A/C is turned on. This allows the ECM time to adjust engine RPM before A/C clutch engages. The ECM will also disengage A/C clutch in full throttle position.
Voltage on circuit 259 to ECM indicates A/C is on. When voltage exists as seen by ECM, the ECM grounds circuit 999 for A/C clutch control relay. Relay contacts close and current flows from circuit 50 to circuit 66.
Ignition voltage exists at high pressure switch. If A/C refrigerant pressure does not exceed certain value, voltage is then supplied to the pressure cycling switch. If insufficient A/C pressure exists, the pressure cycling switch closes. This completes the circuit to A/C clutch. If ECM sees voltage on circuit 259, cooling fans will be activated if vehicle speed, coolant temperature and engine oil temperature are within designated range.
NOTE: Test numbers refer to test numbers on diagnostic charts.
Ensure ECM is controlling A/C clutch control relay.
Check for grounded circuit 999 to ECM.
Check A/C pressure switch operation.
Fig. 4: A/C Clutch Flow Chart (1 of 2)
Courtesy of GENERAL MOTORS CORP.
Fig. 5: A/C Clutch Flow Chart (2 of 2)
Courtesy of GENERAL MOTORS CORP.
WIRING DIAGRAM
Fig. 6: Cooling Fan Wiring Diagram
APPLICATION
ELECTRIC COOLING FAN APPLICATIONS
Application Engine
"Y" Body 5.7L
DESCRIPTION
All FWD and some RWD vehicles use an electric cooling fan. This fan is used for engine and A/C condenser cooling and operates when A/C is on and if engine overheats.
OPERATION
All electric cooling fans operate when engine coolant temperature exceeds a certain value. The ECM completes ground path for the cooling fan relay. Relay contacts then close and complete circuit between fusible link and fan motor. When the engine cools, the switch opens and fan stops. If coolant sensor fails, the ECM will command constant fan operation.
A/C equipped vehicles have a separate signal line to the ECM for fan control. When A/C control switch is "ON", and A/C system low pressure switch is closed, the ECM receives a signal on this line and turns on the cooling fan. The compressor clutch does not have to engage for ECM to turn fan on.
On some models, when engine is off, ECM may turn on the fan relay and run fan for up to 7 minutes. This occurs if hot conditions were present while engine was running. Hot conditions are based on Manifold Absolute Temperature (MAT) signal to ECM, coolant temperature and time from start.
TROUBLE SHOOTING
NOTE: This article contains test charts that are part of General Motors Computerized Engine Controls. Only those charts required to test electric cooling fans are included. Other diagnostic codes may appear while performing electric cooling fan diagnosis. For complete information on General Motors Computerized Engine Control systems, see appropriate article in ENGINE PERFORMANCE section.
CHART C-12, COOLING FAN
Two cooling fans are used, primary fan (driver's side) and secondary fan (passenger's side). Independent fans are controlled by the ECM based on air conditioner head pressure, coolant temperature, engine oil temperature, vehicle speed and A/C operation.
Primary cooling fan is totally controlled by ECM based on inputs from A/C operation, coolant temperature sensor and vehicle speed sensor. Primary cooling fan will be on in the following conditions:
A/C operation exists with high A/C pressure.
A/C operation exists with high A/C pressure and vehicle speed less than 35 mph and coolant temperature is greater than 226°F (108°F).
A/C operation does not exist, vehicle speed greater than 35 mph and coolant temperature is greater than 226°F (108°F).
Primary cooling fan will shut off when the following conditions have existed for 20 seconds:
A/C operation exists with high A/C pressure, vehicle speed is less than 35 mph and coolant temperature is less than 221°F (105°F).
A/C operation does not exist, vehicle speed is greater than 35 mph and coolant temperature is less than 221°F (105°F).
Secondary cooling fan is controlled by the ECM based on inputs from coolant temperature sensor and vehicle speed sensor. ECM will activate secondary cooling fan if primary cooling fan has been operating for 2 seconds and the following conditions exist:
A/C operation exists with high A/C pressure and vehicle speed is less than 50 mph.
A/C operation exists with high A/C pressure, vehicle speed is less than 35 mph and coolant temperature is greater than 235°F (113°F).
A/C operation does not exist, vehicle speed is greater than 35 mph and coolant temperature is greater than 235°F (113°F).
Secondary cooling fan will shut off when the following conditions exist for 15 seconds:
A/C operation exists with high A/C pressure, vehicle speed is less than 35 mph and coolant temperature is less than 226°F (108°F).
A/C operation does not exist, vehicle speed is greater than 35 mph and coolant temperature is less than 226°F (108°F).
Battery voltage is supplied to the fan relay on terminal "E" and ignition voltage to terminal "D."
Grounding circuit No. 409 (relay terminal "F") energizes the primary cooling fan relay and supplies battery voltage to the primary cooling fan motor. Grounding circuit No. 473 (relay terminal "F") energizes the secondary cooling fan relay and supplies battery voltage to the secondary cooling fan motor.
The A/C cooling fan control switch (mounted in the A/C high pressure line) will close when head pressure exceeds 240 psi (16.8 kg/cm2 ). This input causes the ECM to ground circuit No. 409 or 473 if other requirements are met. If a Code 14, 15, 52 or 62 exists, or the ECM is operating in the fuel back-up mode, the ECM will turn on the cooling fans. Cooling fan relays are located on upper radiator support in front of the left wheel panel.
Diagnostic Aids
If an overheating condition is suspected, verify if this is due to actual boilover. If gauge or light indicates an overheat condition, and no boilover is in evidence, inspect the gauge/light circuit for malfunction.
If vehicle is overheating and the gauge or light indicates the same, but the cooling fan is not coming on, check the coolant sensor temperature using a "SCAN" tester. Sensor may have shifted calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system.
Fig. 1: Cooling Fan Circuit Diagram
Courtesy of GENERAL MOTORS CORP.
Fig. 2: Cooling Fan Flow Chart (1 of 2)
Courtesy of GENERAL MOTORS CORP.
Fig. 3: Cooling Fan Flow Chart (2 of 2)
Courtesy of GENERAL MOTORS CORP.
CHART C-10, A/C CLUTCH CIRCUIT
The A/C clutch control relay is ECM controlled to delay A/C clutch engagement approximately 4 tenths of a second after A/C is turned on. This allows the ECM time to adjust engine RPM before A/C clutch engages. The ECM will also disengage A/C clutch in full throttle position.
Voltage on circuit 259 to ECM indicates A/C is on. When voltage exists as seen by ECM, the ECM grounds circuit 999 for A/C clutch control relay. Relay contacts close and current flows from circuit 50 to circuit 66.
Ignition voltage exists at high pressure switch. If A/C refrigerant pressure does not exceed certain value, voltage is then supplied to the pressure cycling switch. If insufficient A/C pressure exists, the pressure cycling switch closes. This completes the circuit to A/C clutch. If ECM sees voltage on circuit 259, cooling fans will be activated if vehicle speed, coolant temperature and engine oil temperature are within designated range.
NOTE: Test numbers refer to test numbers on diagnostic charts.
Ensure ECM is controlling A/C clutch control relay.
Check for grounded circuit 999 to ECM.
Check A/C pressure switch operation.
Fig. 4: A/C Clutch Flow Chart (1 of 2)
Courtesy of GENERAL MOTORS CORP.
Fig. 5: A/C Clutch Flow Chart (2 of 2)
Courtesy of GENERAL MOTORS CORP.
WIRING DIAGRAM
Fig. 6: Cooling Fan Wiring Diagram
Racer
Joined: Feb 2006
Posts: 462
Likes: 0
From: green valley az
Originally Posted by tbone42
I have a 90 pretty much all stock.I know the two fans should come on with the ac on but i have only ever had the one on the drivers side come on never both. where do i start to look and how can i test the fan to make sure it's working.Car getts pretty warm in slow traffic and don't want to cook it thanks for the help Tbone
Melting Slicks
Joined: May 2004
Posts: 2,524
Likes: 10
From: Lufkin Texas
St. Jude Donor '05-'06
I wrote a tech tip on testing the relays and wiring a manual fan switch(s) on a 1990 that is written in layman's terms that may help you out.
https://www.corvetteforum.com/techti...=282&TopicID=2
https://www.corvetteforum.com/techti...=282&TopicID=2
