I have 97 s10 blazer, the ac clutch only in engages when the (after market) electric fan comes on and only shuts off when fan stops,regardless if the switch is on or off. Please help.

 

It is probably the other way around... Most aftermarket fan setups are set to come on full speed whenever the a/c compressor clutch engages.

What switch are you talking about? What are the symptoms you are experiencing? How long does the compressor run for?