Watch your RPM / TACH side - see if the numbers change below ~1,000RPM and as you get there note when the AC wants to "drop".
While you're at Idle - turn the AC on, watch the TACH - it may rise up and "hover" about 850+ or so RPM while the Fan kicks on and the system starts the compressor and the cooling process.
While this is going on, you may see it "seek" up and down on the RPM - nothing excessive or at least anything less than 200 RPM of change is nothing major - because it's trying to find fuel trim.
Now, you have a 2013 - how often have you taken time to clean out the throttle body of gunk? They do tend to collect due to the PCV valve tends to pull oil and fume vapors from the crankcase into the intake manifold so if it's having trouble trying to clear it's throat, might want to remove the snorkel and look down into the bore area for clean metal.
This can also indicate worn or weak hoses that handle Vacuum - like the PCV or the Brake Booster and Air trim regulator - that funky little double diaphragm unit that the booster and snorkel hook up to.
- (do this with the engine off for safety - then you can try and play with it once you are more familiar with the operation of the bore and can keep your fingers out of the plate area)
- - you may also encounter a ring of crud or black goo - that is normal for high-mileage engines
In this - you are checking the throttle body for clear operation - so have someone get into the drivers seat with it in Park and Brake on, with the snorkel off - turn the key to on and then back to off - see if the throttle plate moves and how well it moves - if it seems free - it may need a little cleaning.
Ford does a process of clearing the throttle plate when the system is engaged (Key on) before start and closes or parks the the plate when the key is off. But this also can show sticking or uneven operation - which may mean you might even need a new throttle body because of the electronics are worn in the black plate the throttle plate uses to find and double check throttle plate position - since this thing is a drive by wire - that little black plate does a lot of work when you drive.
- - but it might be prudent to have a mechanic take a look see at this if the engine seems to sag at idle trying to keep up when the AC is on,
- - you can see how pronounced it can get by adding on more accessories like Headlamps - rear defrost. Anything you can do to place a load on the motor and see if it had a problem trying to catch up or now starts to "seek" watching the RPM gauge for this - if it's steady then the issue may be a good cleaning is all that is needed.
