Does double-frying French Fries in an air fryer make it crispier?
I tried out the following procedures with Air Fried french fries and concluded that the best way to make them is to cut, wash and air-fry. 

Note: Any kind of "frying" here refers to air-frying. Also, the potatoes were picked from the same batch, they were cut in exactly the same way with the same width, using a cutting tool.


Blanching in water, freezing in the refrigerator overnight, frying the next day: 



  Resulted in slightly sweet french fries. I don't prefer them sweet.



Blanching in water + salt + vinegar, freezing in the refrigerator overnight, frying the next day: 



  Resulted in slightly sweet french fries. I didn't notice any difference in texture or crispyness as compared to #1.



Blanching in water + salt + vinegar, deep-freezing overnight, frying the next day: Resulted in much sweeter french fries



  Resulted in exactly the same kind of french fries as in #1



Cutting the potatoes, frying them immediately after that: 



  Made the fries stick to each other. Also, the edges of the fries were burnt.



(Best) Cutting the potatoes, washing them with water to remove the surface starch from the potatoes, frying them immediately after that: 



  This made the best result, IMO. It was almost the same as #1, except that it wasn't sweet. The fries were not sticking to each other and crispy.



Cutting the potatoes, frying them in one batch. Waiting for 15 minutes so that they cool down, and the moisture escapes. Then frying them again: 



  The fries felt half-normal, half-hard like crusty cheese. I had to throw the ends of the resulting french fries because they were difficult to chew.


My two cents:


French fries cooking methods from oil-frying don't exactly port over to air-frying.
Air-frying is much quicker and faster. However, it doesn't reach the crispiness of oil-frying. That said, considering the health-benefits, I would go for air-frying any day.
The best way to fry is also the quickest way. Cut, wash, drain, and fry. I've also noticed that adding the spices after they are fried results in better french fries.