Last time I had my system serviced, I watched the tech create a freon cloud when he disconnected. I watched some Youtube videos and learned that low loss fittings like Yellow Jacket SealRight can prevent that. I see they also disconnect one end of the yellow hose and bleed the valves to purge the hoses and manifold of air. How do they know when all the air's gone? They just stopped after a couple of seconds when the hissing stopped. I didn't see any cloud of freon, so it makes me wonder how much the fitting influences this. If you had a low-loss fitting on the yellow hose, would it prevent the air from escaping when you purge? What about normal fittings? How much do they prevent air from escaping? I guess I'm really unclear as to what exactly the fittings do when not connected to anything during this air purge process. Does the low-loss fitting minimize leakage just when attaching/detaching, or is it something more? And what exactly does it prevent the leakage of? Is the intent just to stop liquid refrigerant from escaping? When the Schrader end isn't connected to anything, is there any difference in behavior between a low-loss fitting and a regular one?
I've never used low loss fittings, don't care to either. I simply turn the bottle up side down and as it's shooting a bit of refrigerant out I tighten the hoses down onto the service valves. One hose (side) at a time.
Once a vacuum is pulled and the gauges are closed off, only the yellow hose will be open to atmosphere once disconnected from the pump, the other two will be in vaccum with the system as well as the manifold. Than all you do is purge the yellow hose at the manifold.