i got a 91 camaro rs 305 v8 and it keeps on overheating when i turn on the ac the elctric fan kicks on. somebody told me the it is suppose to do the when the relay or the fan sensor goes out. what can i do to make it work right

i have changed the fan relay and the sensor on the passenger side above the starter.

 

How it works:
Engine Coolant Tem sesor (ECT) sends coolant temp signal to the PCM.
When the proper coolant teemp is reached the PCM operates the fan relay.
Fan relay contacs close and battery voltage is connected to the fan
Fan now runs.

The fan always runs when the AC is turned on, this is normal.
The ETC sensor lives at the front of the intake manifold and has two wires connected to it, one Yellow and one Black. What you changed is probably the temperature gauge sender, which only affects the temperature gauge.

 

the Temp switch for the fan is located under the passenger side head. you can get to it from under the car only. my suggestion is get a Jet fan switch. fixed my 89 without incident