I wish I'd paid more attention to the negative reviews before wasting money on this thing. Although it looks nice out of the packaging, it's all a facade. The problem with mine is in the part that connects to the tire stem. It's designed to shut off the flow of air unless it's pressed onto the tire. Leaving aside the fact that this is not necessary (who cares if air free-flows from the hose when it's not attached to a tire and you press the trigger) the nozzles seals up unless something presses in on it.
My guess is the theory of how this is supposed to work is the little pin inside the tire stem pushes in on the inside of the nozzle to open it and allow airflow. But unless your tire already has some significant pressure or the stem pin has a pretty strong spring, it won't be able to push in the valve in this tool hard enough to allow air to flow. So when you pull the trigger, there a very brief spurt of air which pressurizes the red hose and seals the brass connector on the end. Now no air flows and your tool is locked up.
You have release the trigger and stick a pen or toothpick into this tool to push back the valve and purge the red hose and start again only to have it close up again the moment you pull the trigger.
I don't know what's wrong with the world these days. Everything is a facade of quality over guts of junk in order to squeeze the most optimal, maximal, last fraction of a penny profit from every last sale at any cost and nevermind if it harms the customer. The worst of it is that I would happily pay five times the cost of this tool for something of quality but it just isn't available. We're all reduced to the least common denominator and most of it, like this tool, comes from China.
This thing is going back to Amazon. It's way too much trouble to send back given the price, but if people don't ding Amazon, they're going to continue to sell junk that is easier to take from the packaging to the trashcan than to send it back. So I'm taking whatever steps and time are required to return it.