Your refrigerant is low. Pressure as measured on item 7 should be about 15.September 8, 2012 @9:10am
I just finished doing the A/C diagnosis test and here are the results as follows:
1 (Inside Temp): 91
2(Outside Temp): 96
3 (Left Heater Core Temp) 91
4(Right Heater Core Temp) 87
5(Evaporator Temp): 91
6(Engine Coolant Temp): 190 later 191
7(Refrigerant Pressure) 06
8( Refrigerant Temp) 107 later 111
10(Blower Control Voltage) 4.5
11(Emission Sensor) 1.7
12(Sun Sensor) 4.3
20(Control Current For Auxiliary Fan: 3.2
21 (Engine Speed): 42
22(Vehicle Speed): 00
24(Battery Voltage) 13.1
40(Software Status) 164
41(Hardware Status) 91
43( ???): 136
Freon is a very "slippery" fluid and is difficult to contain. It's not uncommon for MBs to develop leaks after 9 or 10 years.
You will need to have shop check out your system. They will likely evacuate it and then recharge with proper amount of R134a along with a dye. After driving for a week or two, they will be able to inspect and determine where the leak is.
I know from experience that it is frustrating to have expensive A/C repairs when the car is little used and A/C seldom needed.
Some owners will try a temporary solution. Walmart sell R134a and recharging kits. It's easy to do and the A/C may work for a while. But not a long term solution.