Discharging A/C refrigerant?

You're better off having the refrigerant recovered at a shop. The stuff is expensive so they might do that for free. The older R-12 is much more expensive but that hasn't been used since the early 1990s.

When you open something to release R-134, you'll never get liquid that amounts to anything. It boils at a really low temperature. As I recall, it's boiling point is below minus 70 degrees Fahrenheit. Any liquid that comes out will instantly vaporize and disappear.

This brings up an important safety note. Changing state from liquid to vapor is what makes it extremely cold. Professionals wear gloves, safety glasses, and a face shield. Liquid refrigerant can cause blindness and instant frostbite. The only staining you might get is if someone previously added leak-detection dye to the system. That can appear as a fluorescent yellow or green.

As for where you have liquid and vapor, there must never be liquid in the low-side hose. When the system is fully-charged, the evaporator in the dash will be very close to half-filled with liquid. That is the point at which it turns to a vapor, and that's where it gets very cold. If the system is undercharged, that change of state takes place in the high-side hose under the hood. You may see frost develop on that hose. There's no value in having the cooling take place there.

Similarly, if the system is over-charged, liquid can get up into the low-side hose and do the cooling under the hood in that one. Even worse, if that liquid were to slosh into the compressor, it could lock it up for a few hours or even damage the valves and pistons.

Chrysler is the only manufacturer that uses a sight glass on top of their receiver / driers to know when the system has the correct amount of refrigerant. Ford started using them in the 1980s, but they must never be used. (They may have fixed that design issue by 2007 models). When those systems are fully-charged or even over-charged, there will still be vapor bubbles flowing through that window, falsely indicating more refrigerant is needed.

When you don't have a sight glass or it can't be trusted, the only way to know how much refrigerant is in the system is to start with it empty and pumped into a vacuum to boil out any water, then put in the exact amount called for. If you're doing that from small cans, you'll have to guess, but stop adding before you reach what you think is the right amount. If you get nice cool air from the ducts, it's better to stop than to risk over-charging the system. Feel the high-side hose. If there's a spot where it feels really cold, add a little more, and monitor the air temperature at a center duct on the dash. The system should regulate with the evaporator never getting colder than close to 40 degrees. Colder than that and the condensation being removed from the air, (that's where the real comfort comes from), will freeze into solid ice and block air flow. With the evaporator at 40 degrees, it's quite respectable to see 60 degrees at the ducts.

Why are you removing refrigerant? Are you replacing other parts? I should mention too, don't get excited if you see a little bubbling at the charging port when you disconnect the hose. That is normal. Those valves are only intended to hold the refrigerant in while you install the plastic cap. Those have a rubber O-ring inside to do the actual sealing.

I see. I just went through that on a friend's 2015 Expedition with the 3.5L. Setting the timing chains and plastic slides was a nightmare, and plugging in one cam sensor at the back of the left head took two people working together over an hour. We had to disconnect AC hoses too. Your engine should be easier to work on. Let me know how you make out.

We were told to leave the exhaust manifolds bolted to the heads, but that wouldn't work. Luckily all the bolts came out of the heads, but we broke one on each side for the pipes. My trick of heating the stud, then welding a nut to them worked after a few tries. It looked they weren't stuck due to rust. It was that they were in blind holes and had been run in so far that they bottomed out and got extra tight.

I have my fingers crossed for you.

My first thought is to see if you can look through the spark plug hole with a bore scope. Snapon makes a camera with a wand small enough to fit through that hole. Next, if you can push the magnet to a suitable place, stick a thin metal rod down there with some epoxy on the end. Let it clink to the magnet, then go inside for the night. Come back tomorrow and pull the magnet out.

Next thought, if you're as puny as I am, it's very unlikely you're going to bend a valve by rotating the crankshaft by hand. Being small enough to fit through that hole, it's small enough for the piston to not come up high enough to interfere with it. If you feel the crankshaft lock up, just use common sense and stop pulling on the ratchet.

The engine I helped my friend with is one we never want to see again. Everyone says the 5.4L is easier to work on, but even with all the directions we had, very little worked out as it should have. We ended up generating our own procedures, and just kept making adjustments until all the colored links came out right. When everything looked correct, the two camshaft locking tools would not install on one side, yet the engine runs okay with no diagnostic fault codes.

I'm happy to impart as much of my wondrous wisdom as possible, but we should consider starting a new question for the engine problem. This became a private conversation between just the two of us. As such, none of the other experts will see this new problem or have a chance to reply. That may not get you the best help. Some of the people here have some very innovative ideas.

Also, these get categorized by topic for the benefit of others researching similar problems. You may come up with a dandy solution, but others will never get to learn about it unless they also have an AC problem.

Let me know what you come up with.