'90 Vette is overheating
Thread Starter
Racer
Joined: Aug 2008
Posts: 275
Likes: 0
From: Florida
Radiator Fans not coming on with out AC
On my '90, I noticed my radiator fans are not turning on. If i put on the AC, the fans turn on. If I don't use the AC, they do not.
Anyone know what controls them and where I might find the unit in the wiring?
Anyone know what controls them and where I might find the unit in the wiring?
Last edited by stevenhmiller; Aug 28, 2008 at 02:15 PM.
Melting Slicks
Joined: Dec 2004
Posts: 3,284
Likes: 51
From: Jacksonville, FL
St. Jude Donor '08 thru '26
I'm figuring you know that the relays are on the rad shroud on the left side. I'm also thinking that you might want to chect that the temp sensor that feeds the ECM that info is okay, ya have two temp sensors & one is for the gauge and another one is for the ECM.
I'd have to say that since the fans come on w/the A/C that the relays and the high pressure switch in the A/C line are okay. That leaves only the ECM's temp sensor and the wiring from the sensor to the ECM plug that carries that circuit.
HelmInc.com is where you can order up a complete FSM set w/the wiring diagrams....it's a four book set for about $125.00 shipped.
Tom
I'd have to say that since the fans come on w/the A/C that the relays and the high pressure switch in the A/C line are okay. That leaves only the ECM's temp sensor and the wiring from the sensor to the ECM plug that carries that circuit.
HelmInc.com is where you can order up a complete FSM set w/the wiring diagrams....it's a four book set for about $125.00 shipped.
Tom
Racer
Joined: Jan 2007
Posts: 274
Likes: 0
From: Muskogee OK
The coolant temp sensor is located just below the throttle body on an L98.
Also, the ECM will not turn on the fans until coolant temp is at 228.
If you have the C68 Electronic AC control, you can check the digital readout of your temps. Hold in both fan buttons until -00 shows on the AC display. Push the right fan button until -16 shows. Push the AUTO button and the coolant temp temp (in Celcius) will display. If you are metrically challenged like me
, you'll have to google a conversion table for the number.
This should give you an idea if you have a problem.
Also, the ECM will not turn on the fans until coolant temp is at 228.
If you have the C68 Electronic AC control, you can check the digital readout of your temps. Hold in both fan buttons until -00 shows on the AC display. Push the right fan button until -16 shows. Push the AUTO button and the coolant temp temp (in Celcius) will display. If you are metrically challenged like me
, you'll have to google a conversion table for the number.This should give you an idea if you have a problem.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
If i put on the AC, the fans turn on. If I don't use the AC, they do not.
-the ECM can control the fans
-the fan relay is functioning properly
-the fan motor is functioning properly
-the wiring is OK
This leaves the ECM's coolant temp sensor located in the front of the intake base below the TB as the probable problem. Make sure that the connector and wiring is ok.
You can check the sensor by measuring its resistance cold and then hot; the resistance should drop as coolant temp goes up.
