I have several areas I need to focus on now that the winter is finally gone. One of them is slow leaking A/C. I have been recharging the A/C system in my wife’s S90 myself for the past two summers. In 2001 I did it just once, I believe. The freon stayed there for the whole summer. Last summer I had to recharge three times. I expect that this summer I will have to recharge the system even more often. But that is actually not my question. I want to know what is the best way to tell how much of freon I need to put in. Last fall I bought a two-dial (low/high pressure) A/C manifold gauge, but I don't have vacuum pump. So, I can not evacuate the freon from the system; I can only add new freon when the system is running low on freon. Here is what I did tonight. I connected the manifold gauge to the low pressure side and the original pressure reading was in the high 20’s or low 30’s (psi). The compressor was off and not cycling. Then I started to add R134a which activated the compressor. It did not cycle much. Maybe three or four times. After that it stayed on all the time. The pressure settled at about 35 psi. I almost emptied the whole 12oz can of R134a. When I was shaking the can I could fee that there was a little amount of freon left, but it did not want to go in. I waited maybe 4-5 minutes and then shut off the system. So, after the recharge the compressor was always on, the low side pressure was about 35 psi. What does it tell me? Any idea? Do I need to try to add more to the system? (The outside temperature tonight was about 81F. Not very humid.) I am OK with continuing adding freon to the system, but I obviously don't want to overcharge it...

Raphael