Ghost cooling fan problem 1990 c4
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Ghost cooling fan problem 1990 c4
On my 90 vette, I have cooling fans that don't come on during operation. The engine has been taken to 260 degrees and the engine was boiling. Temp was verified, temperature sender has been checked on the side of the block as a precation. Temperature switch under the throttle body was replaced. As part of diagnostics I jumped terminals a and b with a paper clip, both fans worked, I I grounded the blue wire going into relay and could feel and hear relay switch and fans came on on both relays. Checked power at constant and ignition hot wires both are good. Jumped the terminals on the relay and fans came on. I unplugged the temperature switch and fans came on. Everything makes the fans work except automatically..... I don't know what else to check.... help needed bad. AC doesn't work so I can't turn it on.
Last edited by Dswoods3; Jun 11, 2016 at 03:48 PM.
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From: Anaheim CA
Everything changed in 1990 so I'm not 100% sure about all this. It should be the same as earlier years, but might not be...
The ECM controls the fans based on what it sees from the temperature sensor on the front of the intake manifold. You really need a scanner or cable and software to see what the ECM is seeing and responding to. Note that jumpering terminal A to B tells the ECM to go into diagnostic mode and turn on the fans, so it's obviously working.
The ECM turns on the fans when the A/C is turned on. It knows to turn on based on the high pressure switch on the HVAC line (also known as the cooling fan cycling switch). You can simulate the A/C working by disconnecting the connector from this switch.
The ECM controls the fans based on what it sees from the temperature sensor on the front of the intake manifold. You really need a scanner or cable and software to see what the ECM is seeing and responding to. Note that jumpering terminal A to B tells the ECM to go into diagnostic mode and turn on the fans, so it's obviously working.
The ECM turns on the fans when the A/C is turned on. It knows to turn on based on the high pressure switch on the HVAC line (also known as the cooling fan cycling switch). You can simulate the A/C working by disconnecting the connector from this switch.
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Can u describe where that plug would be? When it comes to ac this guy doesn't know squat :/ and does it make a difference that my ac head unit is completely out the car and my compressor is disconnected?
