Dear Forum:

I learned how the scale on our mechanical gauge works. The units are based on the arbitray zeroing 1 atmosphere to 0 inch of mercury and the real pressure is 29.92 in Hg - whatever your mechanical gauge tells you. Mechanical vacuum gauges could be way off at least at very low pressures!

Here is what I did.

- I got a professional grade vacuum pump which gets down to microns of Hg and evacualted the system for about 3 day and achieved a base pressure of about 10 micron with the pressure gauge right on the pump. Which means the pressure in the system was higher but not two orders of magnitude!

- Now I shut off the pump and discounected everything for charging the system.

- I got 3 cans of R134a (340 g each) and a simple charging hose with this piercing valve ...

- I connected the charging hose to the low pressure side and heated up the can with a bowl of warm water. It nicely streamed into the sytem. Beautiful trick.

- I am pretty sure everything went in.

- I tested the system as it says in the manual and measured the temperature at the center console straight after charging. I obtained a lowest temperture of 7.5 deg Celcius. Watching the pressure I could also observe that the compressor switches off as the temp of 7.5 deg Celcius is reached. Can anybody confirm...

Neverless thanks again forum and I have now a ice cold A/C in TN>... Now the car of my wife is fixed and I enjoy working on my 300SD.