penguins25 wrote:when you put your gauges on an ac system you lose freon every time right?
The answer is, yes, you do lose some refrigerant every time. I don't know how much, but I would guess a small fraction of an ounce. The amount of loss would depend on the length of the hoses attached to the manifold gauges. The longer the hoses, the more refrigerant they could contain and vice-versa. Regardless, I believe it would still be a very small amount. You wouldn't want to allow the system to suck this small amount of refrigerant back in, however, as the hoses will also contain some air and moisture, which you don't want in a system.
penguins25 wrote:is this enough to make a difference?
I don't think it would make any difference to a system if you tested it a time or two. Testing three, four, or more times would begin to add up, though, and would depend on the system's total capacity. If a modern system holds, say, 14 ounces (less than one pound), an ounce of loss would be proportionally more significant than on an older system holding, say, 40 ounces (2-1/2 pounds).
penguins25 wrote:is it normal to have little bubbles some times when you unscrew the service caps?
also pressure build up in the caps
is this enough to make a difference?
A minute amount of pressurized refrigerant, dye, and oil under the caps is normal because the caps do the final sealing, not the Schrader valves. I think such a small amount of loss when removing the caps once or twice would make virtually no difference to the total refrigerant charge unless, once again, you removed/reinstalled them many, many times.