Hi guys, i have a dual fan setup from the factory on my 89 formula with tpi. I have a custom prom that has the primary fan kick on at 160 or so. I have my seconday wired to a switch for traffic jams when its super hot. I rarely use the seconday fan b/c it rarely gets that hot in milwaukee. The other day i noticed she was running a little hot...then hotter. I imediatly kicked on my seconday fan and cooled it down. After further inspection i noticed that my primary was not comming on anymore, but when i kicked on my seconday, THEY BOTH RUN. what the hell?? I have the secondary fan relay ground running to a switch. This setup worked perfect until the other day. My question is what the hell could change that they both come on now by kicking in the secondary relay??? As far as I have scene from the wiring, they are two different circuits. Primary runs from ecm, and secondary runs when ac is on or when it gets to 24o from factory.I plugged in my scanner and my cts is working fine. Any ideas where to start. Obvioulsy the relays are fine, if the fans run.??? ANy help wold be great. I just dont understand how 2 fans, on 2 separate circuits could now run together when i flip the switch?

 

Later TG's default when the secondary is turned on before the primary. Look closely at the wiring diagram for the aux fan and you will see a wire that comes from the fan switch for the aux fan and it does loop back the the ECM. You probably have an intermittent primary fan relay, it's very common for them to work off and on. Both coming on when the secondary is turned on is normal.