Ok. I have a 1992 Camaro RS 305 V8. Two problems, Problem #1 I have a single fan and it does work fine with the a/c switch on, but it will not come on by it's self for ex. one time I let it get into the RED before I turned on the a/c switch because I was not sure if my temp. readings were correct so of course the fan never automaticaly came on by it's self so I turned the a/c switch on. So I decided to start geussing on switches and what not. I replaced the fan relay on the driver side firewall. NOTHING. I replaced the Coolant tempature sensor. NOTHING. I replaced the intake air tempature switch. NOTHING. Replaced the coolant fan switch. NOTHING. I don't know what it is but I dont think it's wiring, I have traced it and it seems fine.

 

Your fan comes on with the A/C switch activated? Sounds like the fan switch, even though you've replaced it? Check the wiring to the fan switch. Pull the connector on the fan switch and check with an ohm meter for closed circuit making sure that theres not an open in the wiring. If test okay, do not reconnect the fan switch but rather ground the fan switch wiring and test for fan operation.