57* on a 75* day is not horrible, but it does appear as though you may be low on R-134a. Again, I am no expert, but the way I read that chart above, is that at 75* F, with "Low" (<40%) humidity and a low side pressure reading of 27 to 35 psig you should have 54* to 45* discharge temp from the vents (I assume it is variable between 49*-39* depending on temp, humity % and low side pressure reading). If your humidity is "High" above 40%, then the low side reading should be between 29 and 37 psig, and the discharge temp from the vents should be between 57* and 47* F, again, varying depending on the low side pressure reading, the actual air temp, and humidity level.

That gauge should work fine for reading the low side port. Depending on your humidity, you should get a reading somewhere near 33 or 35 psig. Anywhere under that and it would be my guess that you may need to add some R-134a to get pressure up to a higher level.

Thanks Bill, Bob, two questions I have at this point.

1. How long do I hold the trigger down when allowing the R-134a freon to enter the system?
2. Is it best to charge the system on a cool (below 70 F), warm (70 - 85 F), or hot ( above 85 F)

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I used that same hose and gauge from ID to charge my 10 year old leSabre last summer. I ran it up to the top of the green which is 45 pounds. It goes in slowly so that you can hold the trigger for 15 seconds or so and then let off. I don't recall but it seems to me the gauge reads while the filling goes on.

I put a fan in front of the car blowing up into the condenser to help get a realistic pressure check. I just let the air around the can provide the heat to evaporate the freon 134a and pressure it into the system.

Yup.....I did mine about 15 or 30 seconds at a time, and then let off. I kept testing pressure until I got to 34 psig (from a starting point of 27 psig which for me was the entire can, but it was rather small).

I don't think it matters what type of day or what the temps are when you charge the system, that is what the chart is for.

I hooked up the gauge and pressed the button till the air was out, then I hooked up the can and the gauge read 65. with the A/C at max and temperature at the lowest setting. I pressed the button shook the can, occasionally reved the engine to about 2500 rpm, The gauge started dropping untill it reached 25. I disconnected and read the center vent temperature at 70 d. I hooked up the gauge with freon again, pressed and shook the can and the gauge didn't move. When I disconnected the guage and pressed the button there was still freon in the can. Checked the vent temperature and it was now at 80 d. I started at 57 and ended with 80 d. What did I do wrong?

Kind of unsure what you did, here, Frank. :? It sounds as if you followed Bill'* instructions to hook-up the gauge to the can and purged the can of air, then hooked the fitting to low-side port (the fitting on the larger, upper line) and had an initial reading of 65 psig? If so, that reading is WAY to high to begin with. I am lost as to how it dropped to 25 psig. Adding refridgerant should increase the psig, not decrease it. I am kind of at a loss of where to go from here. If you really have 25 psig in the line, then I would expect 80* at the vents, and that would mean you would need to add refridgerant, but how the heck did you go from 65 psig to 25 in the first place? I really am confused by that.

I guess I would follow Bill'* instructions and try again. Hook up the gauge to the can and purge air. Connect hose fitting to low side port (make sure it is on and connected) then look at the gauge reading. If you get an initial reading of 25 psig or anything below 35 psig, then try adding some refridgerant and keep checking the gauge to see if will rise. It should rise if refidgerant is entering the system.

When you purge for air are you suppost to shake the can or just let all the air out. If you don't shake it and let all that air out aren't you in essance making the can less of a compressed air container. In other words will there be enough compressed air psi to push the freon into the system once conected?

When I purged the can I shook it untill freon was starting to excape. I could have purged it much more if I didn't shake the car before connecting to the large line.

Another question if I may, what would happen if I opened the valve on the large line and let it run dry of all pressure/freon and started over again. I know it'* not good for the enviroment and I would be wearing glove, but what if my second cousin from my long lost grandfather...from my mothers side were to do it. Is that a bad thing?

How many cans do I need from an empty state to fully charge it. I believe I have 4 full cans left.

You purged the can just fine Frank. As far as evacuating the system completely, that is way outta my knowledge base. If it were me, I would get an initial reading, again, and attempt to add R-134a if the system was undercharged. Again, on my car, I started the car and set the A/c to max fan, full cold. I shook the can quite well (my hose/gauge was already attached to the can, but looks exactly the same as the one your using), purged some air from the can (not much really, though), attached the fitting to the low-side port, and got a reading of 27psig. I then squeezed the trigger and for about 15-30 seconds and after each time I stopped depressing the trigger, I shook the can the best I could while it was attached to the port. After several minutes, I could visibly see the pressure rising and I finally ran out of R-134a at about 34 psig, whihc was in spec according to the chart (not too high, not too low). Since then, I have been enjoying cold A/C with no issues. Sorry I don't exactly what is happening or why you got a reading of 65 psig initially tehn it dropped to 25 unless it was overfilled and some refridegerant escaped during your attempt to add. That is why I would liek to see a new reading to see where it is now. Again, at 25 psig is on the low side of being able to work. Mine was at 27 and didn't cool teh air, but those gauges may not be the most accurate.

When you did yours Bob, just it only take one can to fill and what size was that can?

Only took one can to get me from 27 to 34. Not sure on the size, but it wasn't the largest can they sold. I wasn't sure that it was my problem, so I bought the smallest can possible to try it out, maybe 12 ounces...about the size of a can of soda, but wider.