Installed a Hypertech switch (on 200F) a month back and both fans turned on at around 140 and just stay on pretty much all the time. Not wanting the fans to burn out I installed a JET switch (on 195F) and now the fans turned on at 160 and stayed on but now about a week later neither fan turns on except when the A/C is on they both run strong. Hard to believe both switches are faulty, don't know what to try next.

 

Is your temp gauge accurate?

Given the AC uses the same relay(s) to operate the fan that would indicate a problem with the switch
Take the wire off the switch and touch it to the head.(Ign on )
If the fan runs , then the switch is the problem ; if it doesn't you have a problem with the wiring to the switch

 

From what I can tell, it is.

I'll try that. What about the coolant temp sensor by the thermostat housing? What role does that play? I've been under the impression the fan switch is the sole cause of my problem.

 

The CTS gives the engine temp to the computer for it's operations

On a TPI, the fan is controlled by the computer and the fan on temp can only be changed by reprogramming the computer.
If you want to install a aftemarket switch like you are using ,custom wiring is needed to bypass the computer control

On a TBI , the fan is controlled by the fan switch with no input from the computer

 

Custom wiring? Never heard anyone doing anything like that other than replacing the sensor and splicing in a new plug >.<

 

I second what Vetteoz said.

Single fan is only controlled by the fan switch. Dual fan set up, the primary fan turns on from the ECM, secondary fan turns on from the switch. Both should turn on with the AC.

 

So I'll prolly replace the switch again. Should I get a custom chip or new eprom as well? Not familiar with ECM stuff

 

I'm not up to speed on the individual 3rd Gen model differences between models but if the 2nd fan is controlled by the switch then that should be the only one running at the wrong temp off your new switch.
( unless the fan wiring has been modified to run both fans at the same time????? )

 

No wiring has been modified. When the switch was stock they turned on separately at different temps. The original wasn't bad, its just I live in AZ and wanted them on earlier for the heat we have here. With both new switches the fans go off and come on together. No idea