Bad A/C Manifold Quick Couplers? Can't be... Doing something wrong

Ages ago - I was trained on how to deal with A/C systems and Freon - for Aircraft. Been some years… Anyway - my 92 Chev Truck (converted to R134a) hasn’t had working A/C for quite some time. I also have to replace the Transmission - and thought to get the A/C working. Figured it has no Refrigerant. Going to find the leak using some UltraSonic equipment. Going ‘bad boy’ - just hook up the Quick Connects and put 40 psi Air into the system. But you know - if you open the quick connect coupler (just holding it in your hand - not connected to anything) - and blow with your mouth - it is like it is CLOSED. No air can be forced thru. Either opened or closed. You hook them up to the truck - leave the Manifold valves closed - and no movement on the gages, Start the truck up - no gage movement. I did put a straight thread fitting onto the Low side Blue Quick Connect coupler - to plug the Air hose into - and that was like - no air is going anywhere. Take everything Off; and knowing the system is empty - I take a screwdriver wondering if possibly somehow the valve core on the low side is ‘stuck’ - and slightly depress… WHOA - we have Pressure. System is not empty. When the truck is running - the compressor is cycling on and off - waiting for some refrigerant. But the quick connect couplings were hard to put on - but I did get them to clamp down - and will not pull off - before I opened each of the quick connect coupler valves. By screwing them down clockwise all the way - to move the internal pin to depress the low and high side valve core(s). I also recently purchased a set of New Couplers - and they have the exact same thing - of not being able to blow any air thru - either open or closed - with just the quick connect coupler - holding it in your hand. Just blowing some air with your mouth - like how do these work?? Cause they don’t seem to be allowing anything to the manifold - or even actually opening up the system - to check stuff out - and you supposedly can’t put them on wrong - with it being converted to R134a and the different sizes of the two fittings of High and Low. So, I am quite stumped.

A little brevity and some breaks in your wall of text might get you some replies . 58 looks at your post and they just moved on.

That’s sad. I notice in a lot of posts - people going - please explain more; did you do this? Did you do that?.. etc. Since details seem to be important - I give them.

I’ve never had a/c couplings apart, but I think they have valves inside them (in addition to the thread down part,) that require more pressure to open than you can provide with your mouth and lungs. and honestly, with the pressure involved with a/c work, I would highly recommend you stop using your mouth for anything here to avoid any risk of injury.

I’ve never had a coupler get stuck, but they can be difficult. The high side can be quite a bit more difficult if the pressures are high. Turn the screw portion off, and try pushing down on the entire coupler and then releasing the quick release. Perhaps put gloves on first, as well.

Thank you. Probably good suggestion on the mouth. Plus - yeah your lung power doesn’t work. I cleaned the outside of the two fittings this morning (not that they looked terrible) - sprayed the cleaned fittings with silicone; and the two couplers slipped right on; snapped down - and voila - we have pressure reading. Started the truck; watched them cycle a bit. I have to research on what is wrong - but glad I didn’t actually get shop air into it yesterday - since it was not empty. The couplers yesterday - I must not have had fully engaged - even though they would not pull off; and the ring part was down.

Gloves would be good - but they should be special Refrigerant gloves. Any normal gloves of various types - any Refrigerant spray getting on to them - will be soaked up by the gloves - and Freeze them to your hand. Not good. Thank you again for your thoughts and advice.