The engine may be in need of a tune up.
The ac pump may be seized up.
turn the car on
The squealing noise from your car's AC when you turn it on could be due to a worn-out or loose drive belt, which may need to be replaced or adjusted by a mechanic.
If you have the defroster on, the ac comes on automatically.
You have a blocked radiator.
yes it does AC needs some power from engine so it happens....
the ac in the car cools, the fact you have set a higher temperature than the ambient tempereature means that the car's heater is working and so is the ac, if you wish to heat up your car, turn the ac off.
The idle is set too low or there is an electrical problem
if you are in a car turn on the ac or have a portable fan with you
If its dropping RPM's when u turn ur AC on then u need to clean ur Mass Airflow Sensor which will be located on the intake. Use B12
when the AC is on it puts more stress on the engine cause the engine has to now turn the compressor. which in turn adds more heat to the engine.
The AC takes the moisture out of the cabin air and that helps clear the inside of the windshield from moisture faster.