When the A/C or defroster are turned on, the compressor is engaged. That is placing an added load on the engine. The vehicle has what is called an idle air control valve. This system is designed to increase the idle speed and compensate for the added load.
Pay attention to the engine speed when you turn the AC on and off. Pay attention if the engine speed (idle speed) changes a lot when it is on.
If it drops, try servicing the IAC. Here is a link that explains how it's done.
I attached a pic below of the IAC's location. It will be mounted on the throttle body.
Let me know if this helps.
See pic below.
Monday, September 27th, 2021 AT 8:13 PM