What controls cooling fan on when ac is on?

What controls cooling fan on when ac is on?
I don't think AC works the way you think it does. There is nocooling fan in an AC system.. the operation of the engine fan(which draws air through the condenser and radiator) is controlledby a thermal switch, and its operation remains unchanged with theAC on. The blower motor which pushes air through the HVAC ducts isthe same one used for both heat and AC, and is controlled typicallyby a switch.
AC cools by pressurizing and depressurizing the refrigerant andcycling it through the AC system, which causes it to absorb ambientheat and heat drawn from the passenger compartment.. it then cyclesthat heated refrigerant through the condenser, where the heat fromthe refrigerant is rapidly exhanged to the air passing through thecondenser fins, causing a rapid cooling of the refrigerant.
To do this, certain pressures must be maintained in the system, andthis is done by the compressor. Most automotive AC systems use acycling clutch compressor, where the compressor clutch is engagedand disengaged through pressure switches in the system in order toregulate the system pressure.