88 IROC 5.7 TPI. For quite some time, both fans would run as soon as ignition was on. I unplugged secondary fan switch (located in passenger side head between spark plugs 6 and 8) and fans shut off. There appeared to be a short in the switch/sensor so I replaced it.

Turned ignition switch on and no fans. Started car and no fans for a while as it idled. So far so good. Then both fans came on and the dash gauge shot up to max.
As i understand it, the primary fan is supposed to come on when it reaches temp (~180 degrees) and then the secondary fan is supposed to come on when either AC is turned on and/or temp reaches ~220.

Is my understanding correct? Thoughts on why both fans still coming on? Engine didn't run long enough to reach any extreme temps. Dash gauge always appeared to work correctly before replacing secondary fan switch/sendor.

Thanks in advance.

 

Somebody probably wired both fans to come on off the switch. Primary fan is supposed to be actuated by the computer that uses the CTS to tell it what temp the engine water is. If that is not working maybe somebody got lazy and wired them together for the effect you are getting. Trace the wiring to figure out best you can what was done. Have fun!

 

The primary fan is supposed to turn on around 222F and the secondary fan on around 243F. See the following technical article:
https://www.thirdgen.org/electric_co...spec_mod_dual/

It's possible that you bought a secondary fan switch that turns on before 222F, the point where the primary fan supposed to turn on, and that is causing both fans to turn on. If the ECM sees that the secondary fan switch has been activated, it then activates the primary fan.

 

I have seen owners short the AC high pressure switch connector to get both fans to run continuously. That is one way to test the fan motors and relays to rule those components out if one or both fans are not ever coming on. Leaving it that way.... not for me. On my '89 GTA I changed the secondary temp switch to a 200 on / 210 off. The primary fan is controlled by a setting in the ECM. For a while I controlled the primary by placing a 190 on/ 200 off temp switch in the water pump. My pump had a pipe plug in one side which I'm not sure all OE pumps have. ( I replaced my pump a good long while ago.) With the 190 on / 200 off temp switch in the water pump, I wired it to to the primary fan relay 'switched ground' that applies the ground to turn the fan on. Cool running from then on. I ultimately changed the ECM temp with TunerCat, but also had to get a EEPROM adapter to make loading that change easier, but that is another story. Those adapters used to come from Craig Moates, he just recently closed shop. TC at Tunercat.com shows them on his site but likely got his from Craig. :-( Hope any of this helps. -Gerry