Got an A/C question

Only if it's loose in the threads.
Otherwise you have to replace the valve and refill it.
It is exactly like a shrader valve, as in it has it's own little rubber seat in it.
Tightening the valve will only work if the valve is not already seated tightly.
A shrader valve seals around it's outside to the stem it's in, but has another seal that stops the air or in this case coolant from coming back through it until the center pin is depressed.

Sucks huh?

I just had to do one on the wife's BMW.