Some of your questions I should double check....especially about the frost and evaporator tray. I checked it over a week ago, but like I said I had some hospital time since then....and I might not get chance to get out and check those things for a few more days
Where the frost is forming can often give you clues if your system is under or over charged. If it frosts before the evaporator, generally that indicates an undercharged system. Not enough freon in the system to stay in it's high pressure liquid form, it starts to evaporate
before getting to the evaporator. If it frosts
after the evaporator in the outlet line, you likely have a flooded evaporator and the system is over charged.
There is a high pressure side, and a low pressure side to refrigerant systems. That was what I was referring to with the high vs. low pressure question. If your using one of the small cans with the short hose and color coded gauge attached, you should only be able to hook up to the low pressure side anyway. You would need an adapter to hook to the high side
.(NOT that, that's what we want you to do) Good chance you would blow the can up in your hand, the can can't take the pressure a compressor can put out.
A quick course on refrigeration systems to help understand some of the questions and what to look for.
Take a piece of blank paper and draw a diamond standing on it's end, make it big enough to add some labels and notes. (Starting at the top, you should be going clockwise on your drawing.) Alright, at the top point of your diamond draw a small square and label it "Compressor". This is the heart of the system. It takes the low pressure freon gas/vapor and pumps it up to a high pressure gas/vapor and pushes it along to the right of your diamond drawing to the next point which is the condenser. Draw a small square at this point and label it "Condenser". The condenser does just what the name implies, it condenses the high pressure vapor into a high pressure liquid. High pressure also equates to high temperature, high enough to get burnt badly if you get bare skin against any of the metal parts. You can tell if your system is working properly by how many bugs, if any are stuck in the condenser. It gets hot enough to cook them out and they break up and blow away with the wind as you drive. Condenser plugged up with bugs? Good chance the a/c isn't working properly if at all. Another clue on the well being of your system. The condenser also acts as a radiator for the freon and removes a lot of the heat from it, in this case the more the better. Now we carry on to the bottom point of our diamond and draw a small square there and label it "XV" which stands for "expansion valve". The name can be a bit misleading, yes is a valve of sorts. It used to be a valve as we think of them, it would throttle open and close controlling the correct amount of freon to the evaporator, but now with the modern systems, most use a fixed capillary tube. A bit smaller than a ballpoint pen ink reservoir in size. It is sized so just the correct amount of freon can pass through to do the job. It doesn't throttle or change the freon flow so it's referred to as "fixed." And since it took over the job of the expansion valve, the name stuck. We just completed the HIGH PRESSURE side of the system. Make a dashed line from the top point (condenser) to the bottom point (XV) dividing the diamond, and everything on the right side is high pressure. Now, the XV has high pressure liquid freon on oneside, and since the XV is just a small tube with hole in through it, that high pressure freon is just going to come rippin through there to the low pressure side. What happens at this point, is the same thing that happens to a hot radiator if you take the cap off. It is released to a low pressure area and turns to vapor/boils. (Also known as steam for water.) Up until this point the rad cap kept the water in a liquid form even when it was hotter than the evaporation point of 212 F. It can be controlled. Same thing with freon, it can be controlled as well. The main difference being, the freon system is a
internal controlled leak. As the freon comes through the cap tube in a high pressure liquid form, it enters the evaporator core which is a relatively large low pressure area and boils into a low pressure vapor just as the water did when it was released into the low pressure air. This boiling action of the freon is where the cooling effect takes place. We left off at the bottom of our diamond at the XV. Going up to the left to the next point, draw your small square and label it "Evaporator". And as mentioned, the evap is where the cooling action takes place, its the aluminum core up in the dash. From there the cool, or even cold freon vapor is drawn back to the compressor, to start the cycle all over again. The cool returning freon vapor is the only cooling the compressor gets, so it's important that the system has enough freon to do the job. While the diamond drawing works well to visualize the layout of the system, the XV and the evaporator are right next to each other in real life. The system is much more efficient this way, but the diamond layout makes it easier to understand.
Ok, hopefully I didn't muddy the situation, only meant to help you understand the basic system and see why some of the questions were asked. Some may seem a bit offbeat, but there is a reason.
