Ok I searched the threads and could not find this problem anywhere.
89 Firebird Formula with 5.7l.

I had the the engine overheat to red line (260)on the stock gauge. I found out the primary and secondary fans are not coming on. So I began troubleshooting the fans and decided to replace the following items.

Fan Relay Located in the passenger side near the air cleaner,
Coolant Fan Switch located between the 6/8 spark plugs (what a bitch that was) and I was there so why not the
temperature Sensor located on the front of the engine.

I also read somewhere that I may need to reset the ECU so I did so by leaving the battery discounted over night since I was quitting for the evening.

(Notes. recently had transmission replaced and they somehow left the distributor cap spark plug wire off??? fixed, and also installed a new B&M megashifter. Also noticed the battery seems to be dead so I replaced it.)

Well needless to say they do not work.

But when I turn on the AC or Defrost and the Compressor comes on, both fans turn on and it starts to cool down.

• I understand that the secondary fan should come on but both?

1. So what can cause the fans to only turn on when the AC is running?
2. Where to turn to now????

I already thought of wires (shorting) crossing (didnt see anything) and Installing a secondary switch to ground the wiring. (Which i found in previous threads of how to do properly.)

If anyone has had this before please let me know.
\
Thank you
AZFIREBIRD

 

If both fans are running with the A/C, the fan circuits are working. '87 and older, the A/C only kicked on the single (or primary in dual fan cars).
Since you're is '89, both fans run with A/C

The ECM should turn the primary on at 220°F
The fan switch should turn both (like the A/C) fans on at 238°F in the event the ECM does not kick the primary on.

It is not uncommon for the stock gauge to be off slightly.
It is not uncommon for the ECM to read a different temperature from the gauge due to the sensor/sender locations.
There may be an issue with the ECM fan driver.

Jumping the ALDL A-B terminal (flashing check engine codes) with the KOEO (key on engine off), should make the ECM run the primary fan. If not, the ECM isn't controlling the primary fan.

Unplug the fan switch and ground the wire KOEO, it should make the fans run as well.

It seems a bit odd the ECM and fan switch have both failed.

 

So does the sensor in the drivers side head tell the ECM to turn the fans on? Where is the temp sender located? Thanks.

 

Nevermind, I searched.